nir_lower_readonly_images_to_tex: Support non-CL semantics

nir_lower_readonly_images_to_tex: Support non-CL semantics

For non-CL, intrinsic access isn't set, because the image type doesn't
have access qualifier. Instead, the access qualifier is set on the variable.

So, add a mode to this pass which can chase back to the variable in addition
to the intrinsic access. Also, update the variable type and the deref chain
types so everything is consistent, that the tex is accessing a sampler. Note
we can't do this for CL, because void-typed samplers don't exist.

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10356>