Add hidden flag for allowing system app to use BAL permission to launch pending intent in background

Priv-app no longer use its BAL permission to launch background activity by default,
it needs to use this new flag to allow this operation.

Bug: 232921553
Test: PackageInstaller.Session.commit() no longer able to start BAL.
Change-Id: Ifbc642a32dbebdf8854e7e5b1366cb899e971fa7
3 files changed