Use a new lock for the app restriction level settings

Previously we were using a global lock for the app restriction
controller and its trackers, while some of the trackers might be quite
slow.

Bug: 221314897
Test: FrameworksMockingServicesTests:BackgroundRestrictionTest
Change-Id: I0a30b7353f0730f1f1a6836833fc9f8d5db897f2