nir/opt_large_constants: Add Small constant handling

nir/opt_large_constants: Add Small constant handling

Adds handling for constant arrays that can be lowered to
'(imm >> bit_index) & bit_mask' instead of constant loads.

RADV fossils:

Totals from 70 (0.05% of 131205) affected shaders:
Instrs: 31441 -> 31260 (-0.58%); split: -0.59%, +0.02%
CodeSize: 172104 -> 170568 (-0.89%)
VGPRs: 2608 -> 2616 (+0.31%)
Latency: 296687 -> 280859 (-5.33%); split: -5.34%, +0.00%
InvThroughput: 65491 -> 65696 (+0.31%); split: -0.11%, +0.42%
VClause: 671 -> 646 (-3.73%)
SClause: 1014 -> 964 (-4.93%)
Copies: 1742 -> 1564 (-10.22%); split: -10.51%, +0.29%
PreSGPRs: 2039 -> 2036 (-0.15%)
PreVGPRs: 2014 -> 2017 (+0.15%)

Reviewed-by: Faith Ekstrand <faith.ekstrand@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/9000>