Integrate Rescue Party boot loop logic to Package Watchdog

Make Package Watchdog the component that receives calls
about boot events, and decides on whether or not to
perform mitigation action for a perceived boot loop.
The logic for selecting an observer to handle boot loops
is similar to how package failure is handled. The threshold
logic is the same as it was in Rescue Party (5 system server
boots in 10 minutes). Rescue Party maintains its own rescue
levels internally, which map to user impact levels.

Add optional onBootLoop() and executeBootLoopMitigation() methods
to PackageHealthObserver.

Add tests to handle the new cases handled by Package Watchdog.

Test: atest RescuePartyTest
Test: atest PackageWatchdogTest
Bug: 136135457
Change-Id: Ic435e60318e369509975c19a9888741e047803de