gh-92550 - Fix regression in `pathlib.Path.rglob()` (GH-92583)

We could try to remedy this by taking a slice, but we then run into an issue where the empty string will match altsep on POSIX. That rabbit hole could keep getting deeper.

A proper fix for the original issue involves making pathlib's path normalisation more configurable - in this case we want to retain trailing slashes, but in other we might want to preserve `./` prefixes, or elide `../` segments when we're sure we won't encounter symlinks.

This reverts commit ea2f5bcd.