[Android] Refactor indirect references to supported Android dependency versions

[camsim99]

In gradle_utils.dart, we have defined many constants specifying the versions of the Android dependencies that Flutter supports. These are used in the Flutter project templates, in Flutter tooling, and in tests.

However, many of the references to these supported versions are indirect (e.g. we may set _maxKnownAndSupportedGradleVersion = '8.0.2' but write tests in reference to 8.0.2 versus _maxKnownAndSupportedGradleVersion). This issue is to serve as reminder to replace these indirect references with direct ones in the hope that we can lower the amount of effort it will take to support new versions of Android dependencies. See https://github.com/flutter/flutter/pull/131444/files#r1304835861 for context.