[SPIR-V] Map llvm.{min,max}num to GL::N{Min,Max} (#88009)

SPIR-V intsruction selection was mapping the LLVM float min/max
intrinsics to FMin and FMax respectively for GL/Vulkan environments,
which does not match the intrinsics' documented treatment of NaN
operands. This patch switches the mapping to the correctly matched NMin
and NMax operations.

Fixes #87072