Hook the new APIs in StagingManager to PackageManagerNative service

Also note, if a StagedApexObserver is observing through binder, they
might not be able to send the original observing object for
unregistration. As such, for binder observer we clean them up when they
die.

(Note: Unit tests have been removed to resolve merge conflict)

Bug: 187444679
Test: atest StagedInstallInternalTest
Change-Id: Ie2e01b01690a5882574282f3158e454a9b6056e7
Merged-In: Ie2e01b01690a5882574282f3158e454a9b6056e7
(cherry picked from commit 5ac0ee82)