nir: replace undef only used by ALU opcodes with 0 or NaN

nir: replace undef only used by ALU opcodes with 0 or NaN

If undef is consumed by an FP opcode, replace it with NaN to eliminate
that opcode, else replace it with 0, but there are exceptions, such as
when undef is used by stores or phis, it's not touched.

This also contains workarounds for viewperf shaders.

radeonsi:
TOTALS FROM AFFECTED SHADERS (1987/58918)
  Code Size: 5158692 -> 5143796 (-0.29 %) bytes
  Max Waves: 22456 -> 22513 (0.25 %)
  Outputs: 3726 -> 3726 (0.00 %)
  Patch Outputs: 0 -> 0 (0.00 %)

Reviewed-by: Faith Ekstrand <faith.ekstrand@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24059>