Android: Increase targetSdkVersion to 31 (Android 12)

Unlike with Android 11, there should be no downsides to doing
this, so we might as well get this out of the way early.
The main part of the work was already done in 5a1a642.

Source/Android/app/src/main/AndroidManifest.xml

@@ -29,7 +29,6 @@
         android:name="android.permission.VIBRATE"
         android:required="false"/>
 
-    <!-- Once compileSdkVersion is 31, add: android:dataExtractionRules="@xml/backup_rules_api_31" -->
     <application
         android:name=".DolphinApplication"
         android:label="@string/app_name"
@@ -38,6 +37,7 @@
         android:preserveLegacyExternalStorage="true"
         android:allowBackup="true"
         android:fullBackupContent="@xml/backup_rules"
+        android:dataExtractionRules="@xml/backup_rules_api_31"
         android:supportsRtl="true"
         android:isGame="true"
         android:banner="@drawable/banner_tv"