MvxApplication.Initialize runs on main thread
## 🔙 Regression

<!--- Summary description of the regression --->

### Old (and correct) behavior
MvxApplication.Initialize is called on background thread

### Current behavior
MvxApplication.Initialize is called on main thread

### Reproduction steps

1. Fork Mvvm-Cross samples.
2. Update TipCalc app to 9.0.10.
3. Update the SplashScreen's base class from MvxSplashScreenActivity to MvxStartActivity.
4. App.Initialize now runs on the main thread

Example:
https://github.com/NoahSurprenant/MvvmCross-Samples

### Configuration

**Version:** >=9.0.10

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