Enforce minSdk constraint for Android Flutter (#164251)

This commit adds validation for the Android SDK version within the
existing dependency version checker. It introduces a warning when the
SDK version is below a predefined threshold. The validation checks for
the `minSdk` property in the `android` block of the app's `build.gradle`
file. It will warn users if their `minSdk` version is out of Flutter's
supported
range and guide them on how to fix it.

Fixes https://github.com/flutter/flutter/issues/134570

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