Centrally Packages break Visual Studio 2019 build
## 🔙 Regression

The restructure of the build targets break the Visual Studio 2019 build.
Building with cake still works locally and on Azure DevOps.

The following change by @Cheesebaron causes this issue:
https://github.com/MvvmCross/MvvmCross/commit/360c30b858efe979cb2d58915b1b254578f5519c


### Old (and correct) behavior

Able to build MvvmCross Solution with Visual Studio 2019 16.8.3


### Current behavior

`Error occurred while restoring NuGet packages: '' is not a valid version string.`

### Reproduction steps

1. checkout develop
2. git clean -dxf
3. Open Solution and build

This results in this build log:
```
Line 3: Error occurred while restoring NuGet packages: '' is not a valid version string.
Line 3545: 39>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.UI\Resources\MainStyles.xaml.cs(9,39,9,57): error CS0509: 'MainStyles': cannot derive from sealed type 'ResourceDictionary'
Line 3546: 39>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.UI\Resources\BaseTheme.xaml.cs(9,38,9,56): error CS0509: 'BaseTheme': cannot derive from sealed type 'ResourceDictionary'
Line 3547: 39>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.UI\GlobalStyles.xaml.cs(6,38,6,56): error CS0509: 'GlobalStyles': cannot derive from sealed type 'ResourceDictionary'
Line 3548: 39>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.UI\FormsApp.xaml.cs(10,37,10,48): error CS0246: The type or namespace name 'Application' could not be found (are you missing a using directive or an assembly reference?)
Line 3549: 39>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.UI\FormsApp.xaml.cs(17,33,17,40): error CS0115: 'FormsApp.OnStart()': no suitable method found to override
Line 3550: 39>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.UI\FormsApp.xaml.cs(22,33,22,40): error CS0115: 'FormsApp.OnSleep()': no suitable method found to override
Line 3551: 39>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.UI\Pages\ParentContentPage.xaml.cs(7,3,7,18): error CS0246: The type or namespace name 'XamlCompilationAttribute' could not be found (are you missing a using directive or an assembly reference?)
Line 3552: 39>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.UI\Pages\ParentContentPage.xaml.cs(7,3,7,18): error CS0246: The type or namespace name 'XamlCompilation' could not be found (are you missing a using directive or an assembly reference?)
Line 3553: 39>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.UI\Pages\ParentContentPage.xaml.cs(7,19,7,41): error CS0103: The name 'XamlCompilationOptions' does not exist in the current context
Line 3554: 39>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.UI\Views\ChildContentView.xaml.cs(7,3,7,18): error CS0246: The type or namespace name 'XamlCompilationAttribute' could not be found (are you missing a using directive or an assembly reference?)
Line 3555: 39>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.UI\Views\ChildContentView.xaml.cs(7,3,7,18): error CS0246: The type or namespace name 'XamlCompilation' could not be found (are you missing a using directive or an assembly reference?)
Line 3556: 39>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.UI\Views\ChildContentView.xaml.cs(7,19,7,41): error CS0103: The name 'XamlCompilationOptions' does not exist in the current context
Line 3557: 39>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.UI\Pages\MixedNavTab1Page.xaml.cs(12,6,12,21): error CS0246: The type or namespace name 'XamlCompilationAttribute' could not be found (are you missing a using directive or an assembly reference?)
Line 3558: 39>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.UI\Pages\MixedNavTab1Page.xaml.cs(12,6,12,21): error CS0246: The type or namespace name 'XamlCompilation' could not be found (are you missing a using directive or an assembly reference?)
Line 3559: 39>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.UI\Pages\MixedNavTab1Page.xaml.cs(12,22,12,44): error CS0103: The name 'XamlCompilationOptions' does not exist in the current context
Line 3560: 39>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.UI\Pages\MixedNavResultDetailPage.xaml.cs(8,6,8,21): error CS0246: The type or namespace name 'XamlCompilationAttribute' could not be found (are you missing a using directive or an assembly reference?)
Line 3561: 39>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.UI\Pages\MixedNavResultDetailPage.xaml.cs(8,6,8,21): error CS0246: The type or namespace name 'XamlCompilation' could not be found (are you missing a using directive or an assembly reference?)
Line 3562: 39>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.UI\Pages\MixedNavResultDetailPage.xaml.cs(8,22,8,44): error CS0103: The name 'XamlCompilationOptions' does not exist in the current context
Line 3563: 39>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.UI\Pages\MixedNavTabsPage.xaml.cs(12,3,12,18): error CS0246: The type or namespace name 'XamlCompilationAttribute' could not be found (are you missing a using directive or an assembly reference?)
Line 3564: 39>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.UI\Pages\MixedNavTabsPage.xaml.cs(12,3,12,18): error CS0246: The type or namespace name 'XamlCompilation' could not be found (are you missing a using directive or an assembly reference?)
Line 3565: 39>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.UI\Pages\MixedNavTabsPage.xaml.cs(12,19,12,41): error CS0103: The name 'XamlCompilationOptions' does not exist in the current context
Line 3566: 39>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.UI\Pages\MixedNavTab2Page.xaml.cs(12,6,12,21): error CS0246: The type or namespace name 'XamlCompilationAttribute' could not be found (are you missing a using directive or an assembly reference?)
Line 3567: 39>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.UI\Pages\MixedNavTab2Page.xaml.cs(12,6,12,21): error CS0246: The type or namespace name 'XamlCompilation' could not be found (are you missing a using directive or an assembly reference?)
Line 3568: 39>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.UI\Pages\MixedNavTab2Page.xaml.cs(12,22,12,44): error CS0103: The name 'XamlCompilationOptions' does not exist in the current context
Line 3569: 39>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.UI\Pages\MixedNavMasterRootContentPage.xaml.cs(12,3,12,18): error CS0246: The type or namespace name 'XamlCompilationAttribute' could not be found (are you missing a using directive or an assembly reference?)
Line 3570: 39>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.UI\Pages\MixedNavMasterRootContentPage.xaml.cs(12,3,12,18): error CS0246: The type or namespace name 'XamlCompilation' could not be found (are you missing a using directive or an assembly reference?)
Line 3571: 39>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.UI\Pages\MixedNavMasterRootContentPage.xaml.cs(12,19,12,41): error CS0103: The name 'XamlCompilationOptions' does not exist in the current context
Line 3572: 39>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.UI\Pages\NavigationClosePage.xaml.cs(13,6,13,21): error CS0246: The type or namespace name 'XamlCompilationAttribute' could not be found (are you missing a using directive or an assembly reference?)
Line 3573: 39>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.UI\Pages\NavigationClosePage.xaml.cs(13,6,13,21): error CS0246: The type or namespace name 'XamlCompilation' could not be found (are you missing a using directive or an assembly reference?)
Line 3574: 39>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.UI\Pages\NavigationClosePage.xaml.cs(13,22,13,44): error CS0103: The name 'XamlCompilationOptions' does not exist in the current context
Line 3575: 39>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.UI\Pages\ConvertersPage.xaml.cs(13,3,13,18): error CS0246: The type or namespace name 'XamlCompilationAttribute' could not be found (are you missing a using directive or an assembly reference?)
Line 3576: 39>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.UI\Pages\ConvertersPage.xaml.cs(13,3,13,18): error CS0246: The type or namespace name 'XamlCompilation' could not be found (are you missing a using directive or an assembly reference?)
Line 3577: 39>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.UI\Pages\ConvertersPage.xaml.cs(13,19,13,41): error CS0103: The name 'XamlCompilationOptions' does not exist in the current context
Line 3578: 39>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.UI\Pages\MixedNavMasterDetailPage.xaml.cs(13,6,13,21): error CS0246: The type or namespace name 'XamlCompilationAttribute' could not be found (are you missing a using directive or an assembly reference?)
Line 3579: 39>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.UI\Pages\MixedNavMasterDetailPage.xaml.cs(13,6,13,21): error CS0246: The type or namespace name 'XamlCompilation' could not be found (are you missing a using directive or an assembly reference?)
Line 3580: 39>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.UI\Pages\MixedNavMasterDetailPage.xaml.cs(13,22,13,44): error CS0103: The name 'XamlCompilationOptions' does not exist in the current context
Line 3610: 51>C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\MSBuild\Microsoft\NuGet\16.0\Microsoft.NuGet.targets(198,5): error : Your project file doesn't list 'win' as a "RuntimeIdentifier". You should add 'win' to the "RuntimeIdentifiers" property in your project file and then re-run NuGet restore.
Line 3611: 46>C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\MSBuild\Xamarin\Android\Xamarin.Android.Aapt2.targets(164,3): error APT2260: resource style/Theme.AppCompat.Light.NoActionBar (aka com.mvvmcross.playground:style/Theme.AppCompat.Light.NoActionBar) not found.
Line 3612: 46>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Droid\Resources\values\styles.xml(5): error APT2260: style attribute 'attr/colorPrimary (aka com.mvvmcross.playground:attr/colorPrimary)' not found.
Line 3613: 46>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Droid\Resources\values\styles.xml(5): error APT2260: style attribute 'attr/colorPrimaryDark (aka com.mvvmcross.playground:attr/colorPrimaryDark)' not found.
Line 3614: 46>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Droid\Resources\values\styles.xml(5): error APT2260: style attribute 'attr/colorAccent (aka com.mvvmcross.playground:attr/colorAccent)' not found.
Line 3615: 46>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Droid\Resources\values\styles.xml(5): error APT2260: style attribute 'attr/windowNoTitle (aka com.mvvmcross.playground:attr/windowNoTitle)' not found.
Line 3616: 46>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Droid\Resources\values\styles.xml(5): error APT2260: style attribute 'attr/windowActionBar (aka com.mvvmcross.playground:attr/windowActionBar)' not found.
Line 3617: 46>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Droid\Resources\values\styles.xml(5): error APT2260: style attribute 'attr/windowActionModeOverlay (aka com.mvvmcross.playground:attr/windowActionModeOverlay)' not found.
Line 3618: 46>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Droid\Resources\values\styles.xml(5): error APT2260: style attribute 'attr/colorControlNormal (aka com.mvvmcross.playground:attr/colorControlNormal)' not found.
Line 3619: 46>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Droid\Resources\values\styles.xml(5): error APT2260: style attribute 'attr/colorControlActivated (aka com.mvvmcross.playground:attr/colorControlActivated)' not found.
Line 3620: 46>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Droid\Resources\values\styles.xml(5): error APT2260: style attribute 'attr/colorControlHighlight (aka com.mvvmcross.playground:attr/colorControlHighlight)' not found.
Line 3621: 46>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Droid\Resources\values\styles.xml(5): error APT2260: style attribute 'attr/colorPrimary (aka com.mvvmcross.playground:attr/colorPrimary)' not found.
Line 3622: 46>C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\MSBuild\Xamarin\Android\Xamarin.Android.Aapt2.targets(164,3): error APT2062: failed linking references.
Line 3623: 47>C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\MSBuild\Xamarin\Android\Xamarin.Android.Aapt2.targets(164,3): error APT2260: resource style/Theme.AppCompat.DayNight.Dialog (aka com.mvvmcross.playground.forms:style/Theme.AppCompat.DayNight.Dialog) not found.
Line 3624: 47>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.Droid\obj\Debug\100\lp\7\jl\res\values\styles.xml(4): error APT2260: style attribute 'attr/colorAccent (aka com.mvvmcross.playground.forms:attr/colorAccent)' not found.
Line 3625: 47>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.Droid\Resources\values-v21\styles.xml(5): error APT2260: resource attr/colorPrimary (aka com.mvvmcross.playground.forms:attr/colorPrimary) not found.
Line 3626: 47>C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\MSBuild\Xamarin\Android\Xamarin.Android.Aapt2.targets(164,3): error APT2260: resource style/Theme.AppCompat.Light.NoActionBar (aka com.mvvmcross.playground.forms:style/Theme.AppCompat.Light.NoActionBar) not found.
Line 3627: 47>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.Droid\Resources\values\styles.xml(5): error APT2260: style attribute 'attr/colorPrimary (aka com.mvvmcross.playground.forms:attr/colorPrimary)' not found.
Line 3628: 47>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.Droid\Resources\values\styles.xml(5): error APT2260: style attribute 'attr/colorPrimaryDark (aka com.mvvmcross.playground.forms:attr/colorPrimaryDark)' not found.
Line 3629: 47>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.Droid\Resources\values\styles.xml(5): error APT2260: style attribute 'attr/colorAccent (aka com.mvvmcross.playground.forms:attr/colorAccent)' not found.
Line 3630: 47>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.Droid\Resources\values\styles.xml(5): error APT2260: style attribute 'attr/windowNoTitle (aka com.mvvmcross.playground.forms:attr/windowNoTitle)' not found.
Line 3631: 47>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.Droid\Resources\values\styles.xml(5): error APT2260: style attribute 'attr/windowActionBar (aka com.mvvmcross.playground.forms:attr/windowActionBar)' not found.
Line 3632: 47>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.Droid\Resources\values\styles.xml(5): error APT2260: style attribute 'attr/windowActionModeOverlay (aka com.mvvmcross.playground.forms:attr/windowActionModeOverlay)' not found.
Line 3633: 47>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.Droid\Resources\values\styles.xml(5): error APT2260: style attribute 'attr/colorControlNormal (aka com.mvvmcross.playground.forms:attr/colorControlNormal)' not found.
Line 3634: 47>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.Droid\Resources\values\styles.xml(5): error APT2260: style attribute 'attr/colorControlActivated (aka com.mvvmcross.playground.forms:attr/colorControlActivated)' not found.
Line 3635: 47>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.Droid\Resources\values\styles.xml(5): error APT2260: style attribute 'attr/colorControlHighlight (aka com.mvvmcross.playground.forms:attr/colorControlHighlight)' not found.
Line 3636: 47>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.Droid\Resources\values\styles.xml(5): error APT2260: style attribute 'attr/colorPrimary (aka com.mvvmcross.playground.forms:attr/colorPrimary)' not found.
Line 3637: 47>C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\MSBuild\Xamarin\Android\Xamarin.Android.Aapt2.targets(164,3): error APT2260: resource style/Theme.AppCompat.DayNight.DarkActionBar (aka com.mvvmcross.playground.forms:style/Theme.AppCompat.DayNight.DarkActionBar) not found.
Line 3638: 47>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.Droid\obj\Debug\100\lp\7\jl\res\values\styles.xml(2): error APT2260: style attribute 'attr/windowNoTitle (aka com.mvvmcross.playground.forms:attr/windowNoTitle)' not found.
Line 3639: 47>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.Droid\obj\Debug\100\lp\7\jl\res\values\styles.xml(2): error APT2260: style attribute 'attr/windowActionBar (aka com.mvvmcross.playground.forms:attr/windowActionBar)' not found.
Line 3640: 47>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.Droid\obj\Debug\100\lp\7\jl\res\values\styles.xml(2): error APT2260: style attribute 'attr/colorPrimary (aka com.mvvmcross.playground.forms:attr/colorPrimary)' not found.
Line 3641: 47>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.Droid\obj\Debug\100\lp\7\jl\res\values\styles.xml(2): error APT2260: style attribute 'attr/colorPrimaryDark (aka com.mvvmcross.playground.forms:attr/colorPrimaryDark)' not found.
Line 3642: 47>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.Droid\obj\Debug\100\lp\7\jl\res\values\styles.xml(3): error APT2260: style attribute 'attr/colorAccent (aka com.mvvmcross.playground.forms:attr/colorAccent)' not found.
Line 3643: 43>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Uwp\Playground.Uwp.csproj : XamlCompiler error WMC1006: Cannot resolve Assembly or Windows Metadata file 'Type universe cannot resolve assembly: System.Runtime, Version=4.2.1.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a.'
Line 3644: 43>CSC : error CS2001: Source file 'C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Uwp\obj\x86\Debug\App.g.i.cs' could not be found.
Line 3645: 43>C:\Program Files (x86)\Windows Kits\10\bin\10.0.17134.0\XamlCompiler\Microsoft.Windows.UI.Xaml.Common.targets(449,5): error MSB4181: The "CompileXaml" task returned false but did not log an error.
Line 3645: 43>C:\Program Files (x86)\Windows Kits\10\bin\10.0.17134.0\XamlCompiler\Microsoft.Windows.UI.Xaml.Common.targets(449,5): error MSB4181: The "CompileXaml" task returned false but did not log an error.
Line 3646: 50>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.Uwp\Playground.Forms.Uwp.csproj : XamlCompiler error WMC1006: Cannot resolve Assembly or Windows Metadata file 'C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.UI\bin\Debug\netstandard2.0\Playground.Forms.UI.dll'
Line 3647: 50>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.Uwp\Playground.Forms.Uwp.csproj : XamlCompiler error WMC1006: Cannot resolve Assembly or Windows Metadata file 'Type universe cannot resolve assembly: Xamarin.Forms.Platform.UAP, Version=2.0.0.0, Culture=neutral, PublicKeyToken=null.'
Line 3648: 52>CSC : error CS0006: Metadata file 'C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.UI\bin\Debug\netstandard2.0\Playground.Forms.UI.dll' could not be found
Line 3651: 42>C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.TvOS\LinkerPleaseInclude.cs(91,54,91,60): error CS1503: Argument 2: cannot convert from 'MvvmCross.ViewModels.IMvxViewModelLoader' to 'MvvmCross.Views.IMvxViewDispatcher'
Line 3654: 48>CSC : error CS0006: Metadata file 'C:\Projects\OpenSource\MvvmCross\Projects\Playground\Playground.Forms.UI\bin\Debug\netstandard2.0\Playground.Forms.UI.dll' could not be found
```


### Configuration

**Version:** 7.x 

**Platform:** 
- [?] :iphone: iOS
- [x] :robot: Android
- [ ] :checkered_flag: WPF
- [x] :earth_americas: UWP
- [?] :apple: MacOS
- [?] :tv: tvOS
- [x] :monkey: Xamarin.Forms
