nir: Copy-propagate vecN operations that are actually moves

nir: Copy-propagate vecN operations that are actually moves

We were already do this for ALU operations but we haven't for non-ALU
operations.  This changes that.

total NIR instructions in shared programs: 2039883 -> 2022338 (-0.86%)
NIR instructions in affected programs:     1768850 -> 1751305 (-0.99%)
helped:                                    14244
HURT:                                      124

total FS instructions in shared programs: 4083960 -> 4084036 (0.00%)
FS instructions in affected programs:     7302 -> 7378 (1.04%)
helped:                                   12
HURT:                                     51

Signed-off-by: Jason Ekstrand <jason.ekstrand@intel.com>
Reviewed-by: Connor Abbott <cwabbott0@gmail.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>