typing: add type hints to the `opener` attributes and arguments of revlog When making revlog and filelog classes visible to pytype, it got confused quite a bit in `mercurial/revlogutils/rewrite.py`, thinking it had a plain `Callable`, and flagging additional methods on it like `join()` and `rename()`. I couldn't figure out how it reduced to that (and PyCharm flagged `opener` references as `Any`), but this makes it happy. So make this change before making the classes visible. The vfs class hierarchy is a bit wonky (e.g. `filteredvfs` is not a `vfs`), so this may need to be revisited with a Protocol class that covers all of the `vfs` classes. But for now, everything works.