Suppress prevent ringer gesture parent page in search.

The full page verion of prevent ringing is still searchable.

- Created a new controller for parent entry.
- On the child controller, inherit the same getAvailabilityStatus() but
  override AVILABLE_UNSEARCHABLE to AVAILABLE so it becomes searchable.

Fixes: 72748524
Test: existing robotests for PreventRingingPreferenceController

Change-Id: Id2454db110c81b59fa4a98338602b03de0812f8a