Change RenderEngine::drawLayers to take a vector of LayerSettings pointers

Prework for the client composition cache logic which extends
LayerSettings. Passing in a set of pointers will reduce the
amount of copying needed when passing the LayerSettings to
RenderEngine.

Bug: 136561771
Test: atest librenderengine_test libcompositionengine_test
Test: go/wm-smoke
Change-Id: Iba89e5d611256583c46e02d32ed9b0cc58969331