Add SceneTransitionLayout in SysUI

This SceneTransitionLayout contains only two scenes, one default scene
that shows over the keyguard/dream and will be completely blank, then a
communal scene containing the glanceable hub UI. SceneTransitionLayout
handles the gesture detection and animation.

Currently the SceneTransitionLayout covers the whole screen and
prevents swiping up to get the bouncer from working, so I've included a
close button to hide it. Temporary UI will be removed once the bouncer
swipe is fixed.

Change is flagged under the communal_hub flag: b/304584416.

Video: http://screencast/cast/NTc2MTIzNjQ1MTk4MzM2MHw3ZTQyYTU4My0xOA

Bug: 303920627
Bug: 304584416
Test: atest SystemUI:NotificationShadeWindowViewControllerTest
Change-Id: Iecff9f200e2f2e520cdc16a5a2bfad3cc1c5b80c