Adds LayersTrace and assertions to FlickerLib 1/4

- Parses layers trace proto and recreates layer hierarchy.
- Added assertions to test for covered regions and visible regions.
- Added detailed reasons for failures.
- Added functional interfaces and util classes to store results.
- Cleaned up ITransitionMonitor save functions as suggested.

Test: atest FlickerLibTest
Bug: b/64532606
Change-Id: Id65bb65014459ea77735454b5261298c2ac06e3f