nir,spirv: add sparse texture fetches

nir,spirv: add sparse texture fetches

Like SPIR-V and GL_ARB_sparse_texture2, these return a residency code. It
is placed in the destination after the rest of the result. If it's zero,
then the texel is resident. Otherwise, it's not resident.

Besides the larger destination and the residency code, sparse fetches
work the same as normal fetches.

Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7774>