[3.14] gh-132775: Support Fallbacks in _PyObject_GetXIData() (gh-134418)

It now supports a "full" fallback to _PyFunction_GetXIData() and then `_PyPickle_GetXIData()`.
There's also room for other fallback modes if that later makes sense.

(cherry picked from commit 88f8102a8f, AKA gh-133482)

Co-authored-by: Eric Snow <ericsnowcurrently@gmail.com>