We were setting the next-tab properly, but were trying to
read it off the wrong object. Now, going from a cell renderer
attribute mapping to the model, or from an action-name to the
action actually works.
When going from attribute mapping to model, it makes most sense
to go directly to the data tab, and when going from an action
name to the owner, we want to show the actions tab. Make it so.
Add a tab that shows size groups of a widget. The properties
of the size group are available here, as well as the widgets
that are part of the size group. We highlight the widgets in
the application when their row in the inspector is hovered.
Move away from cell editing, and use a popover instead. This makes
it easier to e.g. use a color chooser - there's just not enough room
in a cell for many things.
Much of this code is adapted from tests/prop-editor.c.
Show the actions that are added to GtkApplication and
GtkApplicationWindows, as well as action groups that are
inserted elsewhere with gtk_widget_insert_action_group.
https://bugzilla.gnome.org/show_bug.cgi?id=730095
Moving the inspector into libgtk lets use reuse internals without
having to add public API for everything or inventing awkward private
call conventions.
https://bugzilla.gnome.org/show_bug.cgi?id=730095
