Reduce reliance on Service interface overrides, instead
steering clients to the DreamService-specific lifecycle
hooks:
onAttachedToWindow .. onDreamingStarted ..
onDreamingStopped .. onDetachedFromWindow
The old Dream.java is finally gone now too.
Bug: 7281802
Change-Id: Ib7802c3397fde60ad1132fa49831da182eef4d7a