Add package failure flags to Package Watchdog

This is a prerequisite for adding additional logging of
the Watchdog-triggered rollback reason. Add flags which
indicate the failure observed (native, crash, ANR, explicit
health check). These will be used in the future by
RollbackPackageHealthObserver to map the failure type to the
(new) set of available logging metrics.

Test: atest PackageWatchdogTest
Bug: 138782888
Change-Id: I7e7c5e5399011e2761dada2b989a95c2013307e9