Fix dream -> communal when communal is not available

This change updates the dream user actions model so that it only allows
a start swipe to enter communal scene when communal is available.

Test: atest DreamUserActionsViewModelTest
Flag: com.android.systemui.scene_container
Change-Id: I9b67ca5461b05ea8196a1d312970081550ab8568
3 files changed