Adds a setting for controlling always-on ambient display
until the new ambient display settings screen is implemented.
Also updates DozePreferenceController to use the the
AmbientDisplayConfiguration helper instead of recreating that
logic.
Also adds tests for both doze preference controllers.
Bug: 33279975
Test: Toggle "Settings > Display > Always on", verify ambient display is on / off
Test: make RunSettingsRoboTests
Change-Id: If36356bc29329a4e0732e79db662ffb02c9fc189
