[3.14] gh-141004: Document `Py_HASH_*` macros (GH-141205) (#141225)

* gh-141004: Document `Py_HASH_*` macros (GH-141205)

(cherry picked from commit 3989e12d39bfe2587e5ba80873c37e0c2d449088)
(cherry picked from commit 8cec3d3a9d827aadc7008ab4312121fcf28329c6)

Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>