Feature Flag for restricting PendingIntents by same UID

One of the common cases impacted by BAL blocking are apps that create a
PendingIntent and send it itself. Since both sender and creator have the
same permissions (as they are running as the same UID) and the
PendingIntent is not injected from another app, there should be no
security risk.

Test: atest BackgroundActivityLaunchTest
Bug: 314033453
Change-Id: I584536f1947773fbe26f56b8b72969b82bddace0