The code gets rid of the GtkTreeView and replaces it with a GtkListBox.
Most of the logic is now done via GListModel subclasses.
A big change is that this new list is now tracking updates itself and
doesn't need to be manually updated. All code that used to cause rescans
or add forgotten objects to the tree has been removed.
If objects are missing from the object tree, the logic for tracking them
needs to be added.
The main GDK thread lock is not portable and deprecated.
The only reason why gdk_threads_add_timeout() and
gdk_threads_add_timeout_full() exist is to allow invoking a callback
with the GDK lock held, in case 3rd party libraries still use the
deprecated gdk_threads_enter()/gdk_threads_leave() API.
Since we're removing the GDK lock, and we're releasing a new major API,
such code cannot exist any more; this means we can use the GLib API for
installing timeout callbacks.
https://bugzilla.gnome.org/show_bug.cgi?id=793124
Since setting a clip is mandatory for almost all widgets, we can as well
change the size-allocate signature to include a out_clip parameter, just
like GtkCssGadget did. And since we now always propagate baselines, we
might as well pass that one on to size-allocate.
This way we can also make sure to transform the clip returned from
size-allocate to parent-coordinates, i.e. the same coordinate space
priv->allocation is in.
The sidebar in the object page was using up more space than it deserves.
Replace it with a combo box in the subheader. Now that we have more space,
put the CSS node tree and the style properties in the same page again.
Previously, we were only showing the size of the allocation
and clip area. But there is no good reason to hide the position
of these rectangles, so add them, in the traditional format
of X geometry strings: wxh+x+y
Add yet another tab for showing information about a widget that
does not quite fit into any of the other tabs (not a property,
not style information, etc...).
For now, we show the widget state, as well as the default and
focus widget for windows.
