Make bundle channel even more system reserved

- Apps cannot post to these channels (no bypassing the notif
permission, no diluting the content)
- Don't show the notification runtime permission prompt if
the only channels that exist are bundle channels (not a strong
enough signal that the app intends to send notifications)

Test: NotificationManagerServiceTest
Test: PreferencesHelperTest
Test: NotificationPermissionTest
Test: NotificationManagerTest
Fixes: 373476732
Flag: android.service.notification.notification_classification
Change-Id: I4bdf475e83dfd174482f9ed239276a4e0cdee5fd