Gtk.Template: Allow marking children as "internal-child"
Gtk.Template.Child() now takes a kw only "internal" arg which will be passed to gtk_widget_class_bind_template_child_full().
This makes these children accessible from other templates.
Gtk.Template.Child() now takes a kw only "internal" arg which will be passed to gtk_widget_class_bind_template_child_full().
This makes these children accessible from other templates.