SF: Move state out of DisplayDevice to a new Output class

CompositionEngine::Output holds the composition state of an output. A
CompositionEngine::Display is an output, so it derives from it.

The state is removed from DisplayDevice, with some (temporary) accessors
left behind as there are more changes coming.

The composition related code in SurfaceFlinger is adjusted to however
use the output state.

Test: atest libsurfaceflinger_unittest libcompositionengine_test
Bug: 121291683
Change-Id: Idae2d3d96315538d006b27b56e0a8b566ce0e3b8