Introduces an opt pass that attempts to optimize
load_barycentric_at_{sample,offset} with simpler load_barycentric_*
equivalents where possible, and optionally lowers
load_barycentric_at_sample to load_barycentric_at_offset with a position
derived from the sample ID instead.
Signed-off-by: Simon Perretta <simon.perretta@imgtec.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/37658>
