PreferenceFragment target bindings missing after migration to AndroidX
## 🔙 Regression

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

PreferenceFragment target bindings were removed when we migrated to AndroidX. These classes are missing: https://github.com/MvvmCross/MvvmCross/tree/6.4.2/MvvmCross.Android.Support/V7.Preference/Target and not registered during setup.

See https://github.com/MvvmCross/MvvmCross/discussions/4091

### Old (and correct) behavior

You could access BindValue, BindText, BindClick and BindChecked on Preference types

### Current behavior

These are now gone

### Reproduction steps

### Configuration

**Version:** 7.x

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