zink: start using per-stage flags for new shaders, refcount shader modules

zink: start using per-stage flags for new shaders, refcount shader modules

we don't want to recompile shaders if we don't have to, so we can set bitflags
upon receiving new shader states and then compile only the stages that have
changed while refcounting the unchanged stages

Reviewed-by: Erik Faye-Lund <erik.faye-lund@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5970>