Intercept and ignore all vertical scroll events when renaming or frozen

[jeremypw]

Fixes #1194

Scrolling is inhibited by setting the flags for the scroll controller to intercept all scroll events when renaming starts - the handler then ignores the events.

The keypress controller is prevented from modifying the scroll controller flags during a rename.

It is not necessary to intercept horizontal scroll events in Miller view as the renaming entry is tied to the slot and moves horizontally with it.

[lenemter]

I don't think that's the best solution. The renaming field should scroll along with the view and when typing it should scroll back to that item. Not sure if that's possible to implement in Gtk3

[jeremypw]

@lenemter I don't think that is possible using the builtin editing function of Gtk.TreeView - possibly not in Gtk4 either while we continue to use Gtk.TreeView editable. Once we switch to dynamic views it will no longer be an issue but that is some way off at the present rate of progress. I'm not keen on spending a lot of time on this issue or changing the code too much (e.g. by using a dialog) at this stage tbh.

Is there a valid reason to want to scroll the view in the middle of a rename? This solution is essentially the same as using a modal dialog, preventing interaction with the parent (as far as scrolling is concerned).