nfo directory.

        To ease parsing, this converts a legacy dependency entry into a PEP 508
        requirement string. Like ``_iter_requires_txt_entries()``, there is code
        in ``importlib.metadata`` that does mostly the same, but not do exactly
        what we need.

        Namely, ``importlib.metadata`` does not normalize the extra name before
        putting it into the requirement string, which causes marker comparison
        to fail because the dist-info format do normalize. This is consistent in
        all currently available PEP 517 backends, although not standardized.
        ú