Announcement: New GPS/FB/MLKit packages require MonoAndroid12.0+

[jpobst]

Context: xamarin/AndroidX#444

Beginning with AndroidX.Core 1.7.0, the Google AndroidX Java packages require API-31 (Android 12) in order to compile. Attempting to compile apps using them with previous versions of Android result in the following error:

error APT2260: resource android:attr/lStar not found.
error APT2062: failed linking references.

This can also be seen in the META-INF\com\android\build\gradle\aar-metadata.properties file in core-1.7.0.aar (source):

aarFormatVersion=1.0
aarMetadataVersion=1.0
minCompileSdk=31

As such, all AndroidX packages going forward now require MonoAndroid12.0+.

~All GPS/FB/MLKit packages in this repository depend on AndroidX, and thus these packages must also be bumped to MonoAndroid12.0+ in order to reference the latest AndroidX packages. As such, we have to move the entire GPS/FB/MLKit package ecosystem from MonoAndroid9.0/net6.0-android31.0 to MonoAndroid12.0/net6.0-android31.0. This means if you are targeting MonoAndroid9.0/10.0/11.0, you will not be able to use the latest packages. However the existing packages before this change will continue to work.

Note this only affects the Android version you are "targeting". Applications targeting MonoAndroid12.0 will continue to run on devices running previous Android versions.