layers: Improve DrawState write descriptor update

Validate that stageFlags are the same for a single write update.
Validate that all sampler updates from a single write update are either immutable or non-immutable.
Refactor update contents check to have a loop per switch case instead of switching for each loop iteration.
Added two new validation errors:

DRAWSTATE_DESCRIPTOR_STAGEFLAGS_MISMATCH
DRAWSTATE_INCONSISTENT_IMMUTABLE_SAMPLER_UPDATE
4 files changed