Rescind BAL privilege when ShortcutService sends the callback PI

When AppWidgetManager.requestPinAppWidget is called from a client,
The passed in callback PendingIntent is called from the system
server. This allows the PendingIntent to be able to bypass BAL
checks.

Bug: 278722815
Test: manual test. BackgroundActivityLaunchTest. Regression like
      RequestPinAppWidgetTest, PeopleSpaceWidgetManagerTest, etc.
(cherry picked from commit eb904695)
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:0a0778e96d7da3fa8169abdf9261ed62809539fa)
Merged-In: I2df9de272192c9a149a9ff519c96e6e0e8304040
Change-Id: I2df9de272192c9a149a9ff519c96e6e0e8304040