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.

Bug: 187444679
Test: atest StagingManagerTest
Test: atest StagedInstallInternalTest
Change-Id: Ie2e01b01690a5882574282f3158e454a9b6056e7