fix(gtk): detect modifier keys without cursor movement

[nnyyxxxx]

This fixes a regression where pressing Ctrl while hovering over a link wouldn't detect
the link until the cursor moved.

Tested on both x11 / wayland

Fixes #5191

[mitchellh]

Since your changes are both GTK-specific and not window protocol specific, I believe it'd make more sense to put them in apprt/gtk/key.zig. What do you think?

I haven't vetted the actual approach yet, just something I immediately noticed.

[nnyyxxxx]

Since your changes are both GTK-specific and not window protocol specific, I believe it'd make more sense to put them in apprt/gtk/key.zig. What do you think?

yes, that makes sense. I'll start working on that