Fix the toggle status for show sensitive content switches

We need to make the show sensitive content switch checked by default.
The old implementation misses calling to super.updateState(), which
caused lacking of UI refreshment.
This change also added validation to the preference id that is used
to construct the LockScreenNotificationShowSensitiveController, which
avoids misusage.
Added unit tests to verify that the UI is also updated upon Settings
change, and the preference IDs are verified.

Fix: 392621932
Flag: com.android.server.notification.notification_lock_screen_settings
Test: manual
Change-Id: I31fe602d5b5439515e5fdf5c706b420edaf79042