Implement SLS allowlist using App Compat framework.

TODO (in follow-up):
- modify app compat to check signatures
- add showWhenLocked check (breaks some code which should be fixed first)

Test: locally on device
Test: atest FrameworksMockingServicesTests:CommunalManagerServiceTest
Bug: 203673428
Bug: 203692863
Bug: 203684016
Change-Id: I00e1ee0b04bc5a7fec4a32af883d8d7cfed11c0c