Flutter plugin: migrate Android build to built-in Kotlin

[aleclarson]

Hi! Thanks for maintaining Pulsar.

An application using pulsar_haptics 0.1.0 with Flutter 3.44.x reports:

WARNING: Your app uses the following plugins that apply Kotlin Gradle Plugin (KGP): pulsar_haptics
Future versions of Flutter will fail to build if your app uses plugins that apply KGP.

This is not blocking current builds, but Flutter is warning that KGP application will no longer be supported in a future release / with AGP 9.

The current Flutter Android build still contains:

• the Kotlin Gradle Plugin classpath in the buildscript block (lines 4–14)
• id("kotlin-android") and id("org.jetbrains.kotlin.plugin.serialization") (lines 24–28)
• the legacy kotlinOptions block (lines 65–67)

Would you consider migrating the Flutter plugin to built-in Kotlin? The official Flutter guide recommends:

1. For a release that raises the minimum Flutter version to 3.44 / Dart 3.12, remove the KGP plugin declarations and legacy kotlinOptions, then configure the JVM target through the built-in kotlin.compilerOptions DSL.
2. If older Flutter versions must remain supported, conditionally apply org.jetbrains.kotlin.android only for AGP versions below 9, following the compatibility section of the guide.
3. Remove the serialization Gradle plugin if it is no longer needed by the Flutter Android source, and verify the plugin example with AGP 9 and android.builtInKotlin=true.

Guide: https://docs.flutter.dev/release/breaking-changes/migrate-to-built-in-kotlin/for-plugin-authors

There should be no Dart API change required. We would be happy to verify a release candidate. Thanks!

[piaskowyk]

Glad to hear that you uses Pulsar 🎉 Thank for the report! I'll look at it 🫡

[piaskowyk]

Hey! what do you think about this PR - #287 make it sense for you? I'm open for any feedback 😅