nir: Add nir_shader_intrinsics_pass
Like instructions_pass but specialized to intrinsics. More ergnomic for this extremely common case, and possibly a bit faster by avoiding the extra function call on non-intrinsics.
So it's available for new code. I have scripts to Coccinelle the tree (nice savings in LOC) but @zmike might [redacted] me if I do another treewide this week.
Revival of !10395 (closed) which I regret not merging at the time