[SurfaceFlinger] Add composition unit tests

Adds some simple tests to verify the hardware and software composition
of a range of layer types, using mocks to verify the right calls are
made to the HWC and RE interfaces

Test: atest libsurfaceflinger_unittest
Bug: 76421986
Bug: 76432611
Change-Id: Ic3f81008c2182048851a8ab32388e54ee815927a
7 files changed