Set explicit target when constructing PendingIntent

PendingIntent as part of a notification can be intercepted by
a malicious app and re-fired with crafted intent arguments.
System server should set explicit target for these intents
to avoid it being fired to other apps with system privilege.

Bug: 155183624
Test: atest FrameworksServicesTests:DevicePolicyManagerTest
Test: Set a DO/PO with TestDPC, turn on location, verify notification
      works
Test: set a DO with TestDPC, request remote bugreport and verify
      notifcation works
Change-Id: Ib7d0039c3d07a9d1ccf57e944303353ec9e9b66d