Show a notification when FGS while-in-use permission is restricted.

Change from showing a toast to a notification.

Bug: 136219221
Test: atest cts/tests/app/src/android/app/cts/ActivityManagerApi29Test.java
to trigger the notification.

Change-Id: If22a72fb5a70b14d0b424fbcfe6d1e5c70f2a34d