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.
To run the tests, do:
cd tests/
python run-tests.py
See https://mercurial-scm.org/wiki/WritingTests for
more information on writing tests.