We were updating the state when the back button is pressed, not when
the pages were changed, and so the dialog state was broken if the
user went back by swipe (or means other than clicking the back button).
Fix it by handling updating state when the visible view changes.
- Use GListModel for creation, filter and sorting of shortcut sections
- Use AdwStatusPage instead of handling empty states manually
Fixes#1212#1735#2105#2159#2160#2169
The empty search state looks out-of place due to it being nested inside
a listbox. This is because we can only detect empty states through
gtk_list_filter_func().
Refine it by making the empty search placeholder a child of the main stack.
Introduce an additional helper function to detect when all the listbox
rows would be hidden by the filter.
As a part of https://gitlab.gnome.org/GNOME/gnome-control-center/-/issues/1222
