Update Android SDK from 28 to latest stable version in existing flutter packages.

example: https://github.com/flutter/plugins/blob/master/packages/connectivity/connectivity/android/build.gradle

There is still written "compileSdkVersion 28"

Expected: packages should use the latest stable version.

This issue relates to #54382