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.

ninja all check-all