We add a toolbar view containing a scrolled window.
- We set the margins to 12 instead of 18
- Use AdwHeaderBar
- Set minimum size and default size
- Make resizable so it fits on small screens
See https://gitlab.gnome.org/GNOME/gnome-control-center/-/issues/2624
Previously, there were multiple redundant lists of possible values for
this setting. This uses one struct to define not only all the possible
values, but also anything specific to the alternate characters key, so
this can be used for other modifiers.
This also changes the style of the dialog to use a GtkListBox.