GH-70303: Make `pathlib.Path.glob('**')` return both files and directories (#114684)

Return files and directories from `pathlib.Path.glob()` if the pattern ends
with `**`. This is more compatible with `PurePath.full_match()` and with
other glob implementations such as bash and `glob.glob()`. Users can add a
trailing slash to match only directories.

In my previous patch I added a `FutureWarning` with the intention of fixing
this in Python 3.15. Upon further reflection I think this was an
unnecessarily cautious remedy to a clear bug.