nir/peephole_select: Copy instructions into the block before the if
nir/peephole_select: Copy instructions into the block before the if

Previously we tried to do poor-man's copy propagation as we created the
select instructions.  Instead, this commit just moves the instructions from
the blocks inside the if into the block before.  Copy propagation will take
care of making sure we don't have any extra mov's in there for us.

Reviewed-by: Connor Abbott <71178acffcc112b21e5858656e5751f5e4aa9364@gmail.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler