[RESTRICT AUTOMERGE] Pass correct realCallingUid to startActivity() from startActivityInPackage

Previously startActivity would assume that the system was the calling user when
startActivityInPackage was called. Now the uid of the calling application is
forwarded by the system.

Test: manual; we added logging statements to check the value of realCallingUid
in startActivitiesMayWait when launching the calendar app from the calendar widget
and verified that it was the calendar uid rather than the system uid.

Bug: 123013720
Change-Id: I0ef42c2f89b537a720f1ad5aefac756b0ccac52e
Merged-In: I0ef42c2f89b537a720f1ad5aefac756b0ccac52e