added enabling built-in kotlin

sites/docs/src/content/release/breaking-changes/migrate-to-built-in-kotlin/for-app-developers.md

@@ -296,9 +296,26 @@ kotlin {
 
 ## Validate
 
-Execute `flutter run` or `flutter build apk` to
-confirm that your app builds and
-launches on a connected Android device or emulator.
+Before enabling Built-in Kotlin,
+confirm that you have migrated your application
+and any Flutter plugins it uses.
+
+To enable Built-in Kotlin,
+set the `android.builtInKotlin` property to `true`
+in your `gradle.properties` file:
+
+```properties diff title="<flutter-project>/android/gradle.properties"
+# ...
++ android.builtInKotlin=true
+```
+::::note
+Enabling Built-in Kotlin requires Flutter 3.47 or later.
+::::
+
+After enabling Built-in Kotlin,
+execute `flutter run` or `flutter build apk`
+to confirm that your app builds and launches
+on a connected Android device or emulator.
 
 If your app fails to build because
 you are using an unmigrated Flutter plugin,

sites/docs/src/content/release/breaking-changes/migrate-to-built-in-kotlin/for-plugin-authors.md

@@ -419,8 +419,26 @@ the newly released plugin version:
 
 ## Validate
 
-Execute `flutter run` or `flutter build apk` to
-confirm that your plugin example app builds and launches
+Before enabling Built-in Kotlin,
+confirm that you have migrated your plugin example app
+and any Flutter plugins it uses.
+
+To enable Built-in Kotlin,
+set the `android.builtInKotlin` property to `true`
+in your `gradle.properties` file:
+
+```properties diff title="<flutter-project>/android/gradle.properties"
+# ...
++ android.builtInKotlin=true
+```
+
+::::note
+Enabling Built-in Kotlin requires Flutter 3.47 or later.
+::::
+
+After enabling Built-in Kotlin,
+execute `flutter run` or `flutter build apk`
+to confirm that your plugin example app builds and launches
 on a connected Android device or emulator.
 
 If your plugin example app also applies KGP,