Migrate plugin to built-in Kotlin

I am using `android_id` in my Flutter app.

Starting with Android Gradle Plugin (AGP) 9.0,
support for applying the Kotlin Gradle Plugin (KGP) has been removed.
Because this plugin applies KGP,
it causes a compilation error that prevents my app from building.
Flutter [issue #181383](https://github.com/flutter/flutter/issues/181383)
includes an example of the error.

Flutter has temporarily added support to allow KGP
while apps and plugins migrate to AGP 9.0 or later,
but this support will be removed in a future version of Flutter.

Please migrate this plugin to use built-in Kotlin to
ensure your plugin users can successfully
build their apps in future versions of Flutter.

Here is the Flutter
[migration guide for plugin authors](https://docs.flutter.dev/release/breaking-changes/migrate-to-built-in-kotlin/for-plugin-authors).

Relevant issues:

[Issue #183910](https://github.com/flutter/flutter/issues/183910): Add Disable Built-in Kotlin and new DSL Migrators
[Issue #181383](https://github.com/flutter/flutter/issues/181383): Flutter plugins should support AGP 9.0.0

Start with the plugin's Android build configuration and the linked Flutter migration guide; inspect how the current plugin applies Kotlin. Migrate it to built-in Kotlin, then verify that the plugin builds with AGP 9.0 or later without relying on Flutter's temporary KGP support.

Written by the indexing model from the issue text.