nir: Add a lowering pass for point smoothing

When point smoothing is enabled then this lowering pass will modifies the alpha component of every write to fragment output. Anti-aliased points get rounded with respect to their radius instead of square.

Reviewed-by: Marek Olšák marek.olsak@amd.com Reviewed-by: Pierre-Eric Pelloux-Prayer pierre-eric.pelloux-prayer@amd.com Reviewed-by: Indrajit Kumar Das indrajit-kumar.das@amd.com Reviewed-by: Mihai Preda mihai.preda@amd.com Signed-off-by: Arvind Yadav arvind.yadav@amd.com