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__.

まず、typeshed の ModuleType と pkgutil.extend_path のアノテーションを、Python のモジュールパスおよび pkgutil のドキュメントと比較し、その後、リンクされている mypy と pyright の議論を確認します。文書化された挙動と観測された挙動を反映する、一貫した型の契約を決定します。影響を受けるスタブ間で関連するアノテーションが一致し、extend_path との互換性を維持していれば完了です。