SF: Setup CompositionEngine::Display

Add a Display class to CompositionEngine, and modify DisplayDevice to
create it.

The Display instance holds only some basic data about the display to
start.

Test: atest libsurfaceflinger_unittest libcompositionengine_test
Bug: 121291683
Change-Id: I2a81817c97519c29759cc62b019c9a3c0aee2b93