[Bug libstdc++/106014] Overload std::distance for filesystem::recursive_directory_iterator

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106014

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Also, ranges::advance doesn't use the custom advance for path::iterator. Maybe
we should make path::iterator satisfy the random_access_iterator concept. We
can't do that for directory iterators though, so maybe we want another
customization point for internal use.