Keep granted runtime permissions after restore

[t-m-w]

Marking this as an enhancement because I don't think it's a bug, but it's slightly less-than-ideal behavior.

Steps to reproduce:

1. Make sure an app has runtime permissions granted - for example, for Aves Libre, grant Notifications, Photos and videos.
2. Run a backup that includes the app.
3. From Backup settings, tap the menu and choose Restore.
4. Select the most recent backup.
5. (Optional) Uncheck all apps; then, check the single app you modified so that it's the only one restored.
6. Proceed through to the end of the restore wizard. (No need to restore files.)

Ideal result: The app does not lose its granted permissions.

Actual result: The app loses its granted permissions and will typically prompt for them when opened again.

I am currently not sure if this is feasible to resolve or how stock handles it.