Update the importlib Docs for PEP 684

[ericsnowcurrently]

Documentation

https://docs.python.org/3.12/library/importlib.html#module-importlib.util

• add an entry for importlib.util._incompatible_extension_module_restrictions()

https://docs.python.org/3.12/library/importlib.html#importlib.machinery.ExtensionFileLoader

• update ExtensionFileLoader about when imports may fail

(See https://peps.python.org/pep-0684/ and gh-99113.)

Linked PRs

• gh-107307: Update the importlib Docs for PEP 684 #107400
• [3.12] gh-107307: Update the importlib Docs for PEP 684 (gh-107400) #107413