Defuse notification race around app stops

When abruptly tearing down apps that are in the act of updating their
FGS-related notifications, inherent race conditions can wind up
orphaning notifications on-screen, detached from their original
underlying component lifecycles.  We now mitigate this by doing a
post-teardown sweep of those notifications.

Bug: 228097271
Test: manual
Test: atest CtsAppTestCases:android.app.cts.ServiceTest
Test: atest RunningFgsControllerTest
Test: atest com.android.cts.devicepolicy.DeviceOwnerTest

Change-Id: Iead2976999d6576b3d7854452b7c9986572a4425