[Mesa-stable] spirv: Handle arbitrary bit sizes for deref array indices

[Emil Velikov]

Hi jason,

The commit [1] and it's parent [2] do not apply cleanly for 18.3 and
they are not applicable for the stable branch AFAICT.

If I've misunderstood something and we do need them, can we get a
backport [3]?

Thanks
Emil

[1] bfe31c5e461 nir/builder: Add nir_i2i and nir_u2u helpers which take a bit size
[2] abfe674c54b spirv: Handle arbitrary bit sizes for deref array indices
[3] https://www.mesa3d.org/submittingpatches.html#backports