SF: Refactor onPreComposition

Adds LayerFE::onPreComposition call, and adjusts the existing
implementation inside SurfaceFlinger to use it, in preparation to moving
the loop over to CompositionEngine.

Test: atest libsurfaceflinger_unittest libcompositionengine_test
Bug: 121291683
Change-Id: Ibc0fb1e87d37fabba753f265e70982b5ce70f9f2
4 files changed