Indent Kotlin code with 4 spaces (#43080)

As stated in Kotlin Coding Conventions. Closes #42212

dev/integration_tests/android_embedding_v2_smoke_test/android/app/src/main/kotlin/com/example/android_embedding_v2_smoke_test/MainActivity.kt

@@ -6,7 +6,7 @@ import io.flutter.embedding.android.FlutterActivity
 import io.flutter.embedding.engine.FlutterEngine
 
 class MainActivity: FlutterActivity() {
-  override fun configureFlutterEngine(@NonNull flutterEngine: FlutterEngine) {
-    GeneratedPluginRegistrant.registerWith(flutterEngine);
-  }
+    override fun configureFlutterEngine(@NonNull flutterEngine: FlutterEngine) {
+        GeneratedPluginRegistrant.registerWith(flutterEngine);
+    }
 }

packages/flutter_tools/templates/app/android-kotlin.tmpl/app/src/main/kotlin/androidIdentifier/MainActivity.kt.tmpl

@@ -12,9 +12,9 @@ import io.flutter.embedding.android.FlutterActivity
 import io.flutter.embedding.engine.FlutterEngine
 
 class MainActivity: FlutterActivity() {
-  override fun configureFlutterEngine(@NonNull flutterEngine: FlutterEngine) {
-    GeneratedPluginRegistrant.registerWith(flutterEngine);
-  }
+    override fun configureFlutterEngine(@NonNull flutterEngine: FlutterEngine) {
+        GeneratedPluginRegistrant.registerWith(flutterEngine);
+    }
 }
 {{/useAndroidEmbeddingV2}}
 {{^useAndroidEmbeddingV2}}
@@ -23,9 +23,9 @@ import io.flutter.app.FlutterActivity
 import io.flutter.plugins.GeneratedPluginRegistrant
 
 class MainActivity: FlutterActivity() {
-  override fun onCreate(savedInstanceState: Bundle?) {
-    super.onCreate(savedInstanceState)
-    GeneratedPluginRegistrant.registerWith(this)
-  }
+    override fun onCreate(savedInstanceState: Bundle?) {
+        super.onCreate(savedInstanceState)
+        GeneratedPluginRegistrant.registerWith(this)
+    }
 }
 {{/useAndroidEmbeddingV2}}