Add support for changing save location on Android (#1520)

- Enabled the Android UI path for changing the data folder
- Added Android MANAGE_EXTERNAL_STORAGE permission
- Added an Android flow to request “All files access” before opening the folder picker
- Added code path to resume the folder selection flow after returning from Android settings
- Improved the Android write-probe error message to point users at the required permission

platforms/android/app/src/main/AndroidManifest.xml

@@ -11,6 +11,7 @@
 
     <uses-permission android:name="android.permission.VIBRATE" />
     <uses-permission android:name="android.permission.INTERNET" />
+    <uses-permission android:name="android.permission.MANAGE_EXTERNAL_STORAGE" />
 
     <application
         android:allowBackup="true"