Currently enabling built-in kotlin is not supported in Flutter 3.44. This is because we automatically apply KGP when a subproject (app, plugin used by app etc) does not apply KGP.

This means even when a dev:

1. Ensures their app and any plugin their app uses is migrated to built-in Kotlin
2. Sets android.builtInKotlin=true to enable built-in Kotlin

FGP will still continue to apply KGP, which prevents successful builds. To resolve this, we should add support to enable built-in kotlin. We can check to see if builtInKotlin is enabled and if all subprojects (app, plugins) do not apply KGP.