Add OP_RECEIVE_SENSITIVE_NOTIFICATIONS

This app op is used for the same purpose as the permission of the same
name, but doesn't require the app to declare anything, in order to function.

Flag: android.service.notification.redact_sensitive_notifications_from_untrusted_listeners
Fixes: 346644214
Test: atest SensitiveNotificationRedactionTest
Change-Id: Ieefcbb5f0d6944993d99e929d02a36bb4d7a2b17