Introduce communal scene

This change introduces a communal scene that is placed to the right of
keyguard, and is protected by a config that is disabled by default.

Bug: 300483707
Fix: 300483707
Test: atest LockscreenSceneViewModelTest
Test: atest SceneFrameworkIntegrationTest
Test: atest SystemUiRoboTests:CommunalInteractorTest
Test: enable config_communalServiceEnabled in titan overlay, flexiglass on
(see go/flexiglass-dev-guide), swipe left on keyguard and see communal
scene
Test: without titan overlay change, flexiglass on, swipe left on
keyguard and nothing happens

Change-Id: I43429f68702895ba085cad09749dbfb33264bb60