Add android:exported="true" to activity in Android manifest (#91934)

dev/benchmarks/complex_layout/android/app/src/main/AndroidManifest.xml

@@ -9,6 +9,7 @@ found in the LICENSE file. -->
 
     <application android:name="io.flutter.app.FlutterApplication" android:label="complex_layout" android:icon="@mipmap/ic_launcher">
         <activity android:name="io.flutter.app.FlutterActivity"
+                  android:exported="true"
                   android:launchMode="singleTop"
                   android:theme="@android:style/Theme.Black.NoTitleBar"
                   android:configChanges="orientation|keyboardHidden|keyboard|screenSize|locale|layoutDirection|fontScale|screenLayout|density|uiMode"

packages/flutter_tools/templates/app_shared/android.tmpl/app/src/main/AndroidManifest.xml.tmpl

@@ -5,6 +5,7 @@
         android:icon="@mipmap/ic_launcher">
         <activity
             android:name=".MainActivity"
+            android:exported="true"
             android:launchMode="singleTop"
             android:theme="@style/LaunchTheme"
             android:configChanges="orientation|keyboardHidden|keyboard|screenSize|smallestScreenSize|locale|layoutDirection|fontScale|screenLayout|density|uiMode"