Unify typing for `__path__`?

After the last mypy update v0.920, I started to notice an inconsistency with how the module variable __path__ is typed mainly across typeshed, mypy, and pyright.

In the Python docs it's mentioned as:

`__path__` must be an iterable of strings, but it may be empty.

However the docs for pkgutil.extend_path go on say it's mostly a list (?) cpython/pkgutil.py

    If the input path is not a list (as is the case for frozen
    packages) it is returned unchanged.  The input path is not
    modified; an extended copy is returned.  Items are only appended
    to the copy at the end.

From my point of view, it isn't entirely clear what the "correct" type should be. Some points to consider though:

• In most cases it seems to be a list[str].
• It was mentioned here however that it can sometimes also be a MutableSequence[str]
• The __path__ type should be valid as first argument to pkgutil.extend_path. At the moment that only applies to list[str] but obviously the argument type for extend_path could be changed to, for example, accept a TypeVar bound to Iterable[str] instead.
• It seems to be fairly common (and safe ?) to access the at least the first item of __path__ via __getitem__.

Beginne damit, die Anmerkungen von typeshed ModuleType und pkgutil.extend_path mit der Dokumentation zu Python-Modulpfaden und pkgutil zu vergleichen, und prüfe anschließend die verlinkten Diskussionen zu mypy und pyright. Bestimme einen konsistenten Typvertrag, der das dokumentierte und beobachtete Verhalten widerspiegelt. Als abgeschlossen gilt die Aufgabe, wenn die relevanten Anmerkungen in den betroffenen Stubs übereinstimmen und mit extend_path kompatibel bleiben.