nir/builder: Add nir_umod_imm helper

nir/builder: Add nir_umod_imm helper

Like nir_udiv_imm, we can do a similar power-of-two trick. It's also really
convenient.

v2: Assert reasonable bounds on the modulus (Faith).

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl> [v1]
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com> [v1]
Reviewed-by: Faith Ekstrand <faith.ekstrand@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/22010>