nir/builder: Add a select_from_ssa_def_array helper

This is an operation we have to do already for nir_vector_extract and
I'm about to do something very similar for matrix columns.  Having a
more generic helper is useful.

Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6479>
1 file changed