SF: Move/Refactor prepareFrame to CompositionEngine

This refactors both the SurfaceFlinger::prepareFrame() and
HWComposer::prepare() logic, moving things to to
compositionEngine::Output and compositionEngine::Display.

Along the way, the composition related state is moved out of HWComposer
up to compositionengine::OutputCompositionState.

As there were some subtleties, tests are also added to cover the
refactored logic.

Test: atest libsurfaceflinger_unittest libcompositionengine_test
Bug: 121291683

Change-Id: I2713e9e52751ca0523f6348ffdb51ead8bca5235