Navigate filtered nodes with arrow keys + smaller cleanup

[eibx]

I've added the option to use up and down arrows to select the previous and next filter matches.

I've also removed code relating to _tree_filter_typing.

As far as I can see, _tree_filter_typing and _tree_filter_visible are always in sync (always both true or false).

And because of this an early exit in on_key:

if not self._tree_filter_visible:
    # Pass to next mixin in chain (e.g., AutocompleteMixin)
    super().on_key(event)  # type: ignore[misc]
    return

I can't see how any of the not self.tree_filter_typing statement could be reached.

Again thanks for your work 👍

[Maxteabag]

Hi. Thanks for the PR. I have tested the code but there seems to be some jumping around the nodes. It doesn't feel very intuitive.

[eibx]

The behavior is taken from how the database browser in Rider works. But I now see that the use case in Rider is a bit different, since it doesn't remove the nodes when you search. So jumping around the nodes is more important.

With that in mind and if you feel it's unintuitive, I think we should just close this PR. But I do feel the clean up is still relevant :)

riderdemo.mp4