Create parent class for permission enforcement annotation detectors

Introduce AidlImplementationDetector - an abstract class for detectors
that analyse methods implementing generated AIDL interface stubs.

Refactor ManualPermissionCheckDetector into
SimpleManualPermissionEnforcementDetector that inherits from
AidlImplementationDetector.

Bug: 260314719
Test: SimpleManualPermissionEnforcementDetectorTest
Change-Id: I6221be50b3b358885404894ba158797bb8ea85e4