Organize Fullscreen tasks

Fix a bug where taskinfo changes weren't recording the
changes.

Add FullscreenTaskListener which is very basic and just
shows surfaces on appear. Fullscreen works fine with
this much because the surfaces are always at 0,0
anyways.

Bug: 162499076
Test: Existing tests pass, phone works like normal
Change-Id: I606bc1cbc85c33c4fc40baf6b3080a1eaa37550c