nir/nir_lower_vec3_to_vec4: Use the nir_shader_instructions_pass() helper

Extracts some per-impl code to nir_lower_vec3_to_vec4 and then
converts to use the nir_shader_instructions_pass helper.

Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Reviewed-by: Emma Anholt <emma@anholt.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11683>
1 file changed