Adding flexible update support

[alexstelya]

Xamarin.Google.Android.Play.App.Update.Ktx replaced with Xamarin.Google.Android.Play.Core

[HavenDV]

Please study:
#2

The main problems with this approach are:

• Although flexible updates are supported, there is an issue here with Android 14 not working
• Core includes a lot of unnecessary stuff when Google's recommended approach now is to use modular packages

[HavenDV]

This seems to have been fixed with the update to net 9