☔ [AGP 9] AGP 9.x Fully Tests newDsl in CI #189407

AGP 9.x fully tests newDsl when all test apps and tools (ex: for accurate indexing in Android Studio for engine contributors) in flutter/flutter and flutter/packages have been upgraded to AGP >= 9 and are strictly opted out of newDsl or strictly opted into newDsl.

Core Upgrades to AGP 9 opted out of newDsl

• [AGP 9] Update flutter/flutter to AGP 9.x for Flutter 3.44 #179644
• [AGP 9] Migrate All Plugin Example Apps to Built-in Kotlin #187325

On AGP 9 and opted into newDsl

• ☂ Migrate Flutter Android Gradle Plugin to the AGP "newDsl" #180137 (prereq)
• Use Migrator Tool to Automatically Opt-in to newDsl in 3.50 #189236