LiveData support for PermissionControllerService

Change the PermissionControllerServiceImpl to be able to use the new
LiveData backend. For now, only CountPermissionApps utilizes these.
SmartUpdateMediatorLiveDatas now support observers asking to be notified
when stale values become non-stale.

Test: Manual for now, automated in progress
Bug: 136501318
Fixes: 145628696
Change-Id: Ic82e6af0848a6942cbdd9290f4fe3ae0153d02e5