Add background to Glanceable Hub in scene container

Reuse existing composable in CommunalContainer for CommunalScene, which
gives it a background and all the good stuff added later on. Also
declared basic transitions. Note that they do not match UX specs
perfectly.

Test: verified manually that background and keyguard elements like lock
      icon and charging status show up in Glanceable Hub
Fix: 339448760
Flag: com.android.systemui.scene_container
Change-Id: Iec37367ea22b22fcec8d7bf76f35cf2218d9dbdd