nir/lower_vec_to_movs: Properly handle source modifiers on vecN ops
nir/lower_vec_to_movs: Properly handle source modifiers on vecN ops

I don't know of any piglit tests that are currently broken.  However, there
is nothing stopping a vecN instruction from getting source modifiers and
lower_vec_to_movs is run after we lower to source modifiers.

Reviewed-by: Eduardo Lima Mitev <86e6f0c9eba14994f25948ad50c226b324e9fa92@igalia.com>
Reviewed-by: Matt Turner <789b315743a28dd066a4ba1459c35951c291d8a6@gmail.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler