SF: Carve out LayerHandle

Move LayerHandle outside of layer so it can
be used with the new LayerLifecycleManager.

Make Handle fields like layer private and provide
access functions so callers have to safely cast
from a binder instead of directly casting it.

Add layerid to LayerHandle since we want to
expose the layer class in fewer places.

Finally fold LayerCleaner class into LayerHandler.

Bug: 238781169
Test: presubmit

Change-Id: I86e08050cfcc89d68e6ed8fa0e8ff30063cf3603