Adding required annotations to mark SystemApi

Mark the required hidden APIs before marking the classes as SystemApi.
Need to fix the lint errors before creating SystemApi.

Bug: 361126781
Test: atest PackageWatchdogTest; atest RollbackPackageHealthObserverTests
Flag: EXEMPT refactor
Change-Id: Ia8a4e24372cd8d17f495a493e24759b1b0df6418