Hide the status bar dream overlay when low light is active.

We pipe the component name of the currently active dream into the
overlay service, and when the active dream is lowlight, we hide the
status bar.

Test: atest DreamOverlayStateControllerTest
Test: atest DreamOverlayStatusBarViewControllerTest
Test: manually on device by entering/exiting low light and ensuring the
status bar is hidden
Fixes: 245386662

Change-Id: I22973538bea19ef108360a319c70c878cfd81800