Need to track API removals, mark bindings with [UnsupportedOSPlatform]

[jonpryor]

Context: https://developer.android.com/sdk/api_diff/23/changes

Sometimes, Android removes APIs. For example, API-23 removed the android.Manifest.permission.CLEAR_APP_USER_DATA field.

We still list this field, though: Android.Manifest.Permission.ClearAppUserData field

Is there a way for us to automatically detect such removals? If so, we should add UnsupportedOSPlatformAttribute to those members.

[jpobst]

We do already track this data, however we don't currently do anything with it.

We modified api-merge to add removed-since in dotnet/android#8897.

Here is the excerpt from https://github.com/dotnet/android/blob/main/src/Mono.Android/Profiles/api-Baklava.xml:

<field deprecated="not deprecated" final="true" name="CLEAR_APP_USER_DATA" jni-signature="Ljava/lang/String;" static="true" transient="false" type="java.lang.String" type-generic-aware="java.lang.String" value="&quot;android.permission.CLEAR_APP_USER_DATA&quot;" visibility="public" volatile="false" removed-since="23"></field>

We would need to modify generator to process this data and add the appropriate [UnsupportedOSPlatform] attribute.