chore(android): migrate plugins to built-in Kotlin

[Aricatos]

Summary

• migrate all 22 Android plugin modules away from applying the Kotlin Gradle Plugin
• replace legacy kotlinOptions blocks with kotlin.compilerOptions
• raise the package floor to Flutter 3.44 / Dart 3.12, as required by Flutter's migration guide
• migrate the example app and add stable plus Flutter 3.47 beta Android build lanes

Closes #888.

Validation

• flutter pub get succeeds for the full example workspace
• a focused consumer using google_mlkit_barcode_scanning, google_mlkit_commons, and google_mlkit_text_recognition builds a debug APK on Flutter 3.44.8 without the legacy plugin-KGP warning
• all 22 Android plugin build files contain the compiler-options DSL and none applies or declares KGP
• git diff --check passes

The full all-package example build progressed through native/Kotlin compilation without an emitted error but exceeded a 15-minute local validation bound. The new CI jobs are intended to complete that matrix, including AGP 9 built-in Kotlin on Flutter 3.47 beta.

Release note

This intentionally leaves package version and changelog headings to the maintainers so the migration can follow the final pre-Flutter-3.44 compatibility releases discussed in #888. Each migrated package's eventual release notes should mention the Flutter 3.44 / Dart 3.12 minimum and built-in Kotlin migration.