[3.14] GH-133789: Fix unpickling of pathlib objects pickled in Python 3.13 (GH-133831...

[3.14] GH-133789: Fix unpickling of pathlib objects pickled in Python 3.13 (GH-133831) (#140276)

GH-133789: Fix unpickling of pathlib objects pickled in Python 3.13 (GH-133831)

In Python 3.13 (but not 3.12 or 3.14), pathlib classes are defined in
`pathlib._local` rather than `pathlib`. In hindsight this was a mistake,
but it was difficult to predict how the abstract/local split would pan out.

In this patch we re-introduce `pathlib._local` as a stub module that
re-exports the classes from `pathlib`. This allows path objects pickled in
3.13 to be unpicked in 3.14+
(cherry picked from commit f4e51f253ad6c27583438f6182c33cf368bfa45f)

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