Rename CommunalSceneKey.Foo to CommunalScenes.Foo

This CL changes the communal scenes accessors to CommunalScenes.Foo
instead of CommunalSceneKey.Foo, making them normal `val` instead of
objects. This will make the removal of the fork of STL SceneKey easier.

Bug: 293899074
Test: m sysuig
Test: m SystemUITests
Flag: N/A
Change-Id: Ide515fcf45e3fa757513f869bb5700d2c259436c