SF: Merge EffectLayer into BufferStateLayer

This makes all the Layer instances a BufferStateLayer. The layer can
draw effects or hold a buffer. If the caller tries to do both, drawing
a buffer takes precedence.

Test: go/wm-smoke
Test: presubmit
Bug: 238781169

Change-Id: Ied68cd1ed7399f6408bd24d9e0220707d6a3a2ab
9 files changed