SF: Change RenderEngine ownership

This change allows multiple instances of CompositionEngine to use
the same RenderEngine instance which enables creating new instances of
CompositionEngine to run off the main thread. This will be used in the
refactor of SurfaceFlinger::renderScreenImpl to generate LayerSettings
via CompositionEngine.

Bug: 238643986
Test: presubmits

Change-Id: I0c8dc30e091578d0d77afb434a52038db6e82288