Fragment shaders with side effects need to be lowered to ensure they execute for
all shaded pixels but no helper threads. Add a lowering pass to handle this.
Fixes dEQP-GLES31.functional.shaders.opaque_type_indexing.atomic_counter.const_literal_fragment
Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/21712>
