Policy per https://flutter.dev/go/android-dependency-versions.

https://github.com/flutter/flutter/issues/140913

~Still a WIP while I clean up some error handling, remove some prints, and figure out a Java test (more difficult than the others because I believe we can only install one java version per ci shard).~

~Also it looks like there are errors that I need to fix when this checking is applied to a project that uses the old way of applying AGP/KGP using the top-level `build.gradle` file (instead of the new template way of applying them in the `settings.gradle` file).~ Done, this is why [these lines exist](https://github.com/flutter/flutter/blob/9af6bae6b9a8d7a8a363467b834f52bfc64c9336/packages/flutter_tools/gradle/src/main/groovy/flutter.groovy#L72-L88) in `flutter.groovy`. They just needed to be added