Store layer snapshot in LayerRenderArea

Accessing the layer snapshot from a RenderArea lessens the
dependency on getting the layer snapshot from SF's
mLayerSnapshotBuilder, which needs to run on the main thread.

Bug: b/294936197
Test: atest SurfaceFlinger_test
Change-Id: I7c2a77a432ddae3f7bdd39311a3a505aa8f763d6
5 files changed