[3.13] GH-119169: Implement `pathlib.Path.walk()` using `os.walk()` (GH-119573) ...

[3.13] GH-119169: Implement `pathlib.Path.walk()` using `os.walk()` (GH-119573) (#119750)

GH-119169: Implement `pathlib.Path.walk()` using `os.walk()` (GH-119573)

For silly reasons, pathlib's generic implementation of `walk()` currently
resides in `glob._Globber`. This commit moves it into
`pathlib._abc.PathBase.walk()` where it really belongs, and makes
`pathlib.Path.walk()` call `os.walk()`.
(cherry picked from commit 7ff61f51b6f75315291419269295a8ac3933397b)

Co-authored-by: Barney Gale <barney.gale@gmail.com>