SF: Move management of HWC layers to compositionengine::OutputLayer

OutputLayer creates a HWC layer (if appropriate) on initialization, and
the HWC layer is destroyed with the OutputLayer.

Removes all explicit calls to create/destroy the HWC layers from the front-end
Layer code, and a few other places.

A call is also added to destroy all OutputLayers before switching in or
out of VrComposer mode. This change already marked the geometry as dirty
-- this just ensures all the HWC layers are recreated.

Test: atest libsurfaceflinger_unittest libcompositionengine_test
Test: atest dvr_display-test
Test: atest CtsViewTestCases
Bug: 121291683
Bug: 124537779
Change-Id: Ib7aec9e998ed5481d2753d19b061ba922e54bfe0