Metal will prematurely discard fragments with side effects even if those side effects happen before the discard. Work around this by making said discards "optional". Reviewed-by: Arcady Goldmints-Orlov <arcady@lunarg.com> Signed-off-by: Aitor Camacho <aitor@lunarg.com> Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/38741>