Remove a boatload of "or %NULL" from nullable parameters
and return values. gi-docgen generates suitable text from
the annotation that we don't need to duplicate.
This adds a few missing nullable annotations too.
After the :can-focus change in the previous commit, widgets
need to set suitable focus and grab_focus implementations
to implement the desired focus behavior.
This commit does that for all widgets.
This is an automated change doing these command:
git sed -f g gtk_widget_set_has_window gtk_widget_set_has_surface
git sed -f g gtk_widget_get_has_window gtk_widget_get_has_surface
git sed -f g gtk_widget_set_parent_window gtk_widget_set_parent_surface
git sed -f g gtk_widget_get_parent_window gtk_widget_get_parent_surface
git sed -f g gtk_widget_set_window gtk_widget_set_surface
git sed -f g gtk_widget_get_window gtk_widget_get_surface
git sed -f g gtk_widget_register_window gtk_widget_register_surface
git sed -f g gtk_widget_unregister_window gtk_widget_unregister_surface
git checkout NEWS*
