zink: add ntv handling for ARB_sample_shading

this involves variable handling and decorations as well as a weird bitcast
for the array[1] gl_SampleMask in spirv

Reviewed-by: Erik Faye-Lund <erik.faye-lund@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7192>
1 file changed