OMITTED_NAMED_ARG and OMITTED are a confusing burden:
It puts the burden on developers to pick the right one of the two
They can be interchanged without introducing a compile failure or other error
Picking the wrong one is leading to incorrect docs
They are redundant, because the correct one can already be determined by the surrounding type
Fix all issues by making them an alias of each other; Pick the right one based on the outer type.Backport of core#26706.
Depends on D16314.