ZenModeBackend gets newest notification policy

Previously, notification policy wouldn't be updated
so behavior zen mode settings pages wouldn't update
when an app changed the notification policy.  Now
notification policy will be updated on updateState of
each AbstractZenModePreferenceController.

Bug: 70662324
Test: make RunSettingsRoboTests -j40
Change-Id: Ibee20e4f27e0c833e05230ea8a3ea2cc75ae6bf0