Marking isApex and isApkInApex as SystemApi

RollbackPackageHealthObserver is using this apis.
isApex: to determine if we need to enable two-phase rollback
isApkInApex: To check if rollback is available for package
More Details: go/v-crashrecovery-module-design-doc

Bug: 354693320
Test: m
Flag: android.crashrecovery.flags.enable_crashrecovery
Change-Id: Ie63b29bb7f6f73831607932eccef6869445e54f3