[Overlay] Adjust Media Controls button size and position

- Reuse dream bottom affordance specs to resize the Media Controls
  button, so it has a consistent look with Home Controls button.
- Refactor Home Controls complication to remove the wrapper of the
  ImageView. Also removed the top/bottom margin as complication layout
  engine will take care of spacing.

Bug: b/273545893
Test: enable media controls, Home Controls button and play music.
Test: atest DreamHomeControlsComplicationTest

Change-Id: I28291e0b694666ded7d86b4cf619dd24188f3f90