glsl,nir: Switch the enum representing shader image formats to PIPE_FORMAT.

glsl,nir: Switch the enum representing shader image formats to PIPE_FORMAT.

This means you can directly use format utils on it without having to have
your own GL enum to number-of-components switch statement (or whatever) in
your vulkan backend.

Thanks to imirkin for fixing up the nouveau driver (and a couple of core
details).

This fixes the computed qualifiers for EXT_shader_image_load_store's
non-integer sizeNxM qualifiers, which we don't have tests for.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com> (v3d)
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3355>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3355>