app, libgimp*, modules: don't use g_type_class_add_private() ...

... and G_TYPE_INSTANCE_GET_PRIVATE()

g_type_class_add_private() and G_TYPE_INSTANCE_GET_PRIVATE() were
deprecated in GLib 2.58.  Instead, use
G_DEFINE_[ABSTRACT_]TYPE_WITH_PRIVATE(), and
G_ADD_PRIVATE[_DYNAMIC](), and the implictly-defined
foo_get_instance_private() functions, all of which are available in
the GLib versions we depend on.

This commit only covers types registered using one of the
G_DEFINE_FOO() macros (i.e., most types), but not types with a
custom registration function, of which we still have a few -- GLib
currently only provides a (non-deprecated) public API for adding a
private struct using the G_DEFINE_FOO() macros.

Note that this commit was 99% auto-generated (because I'm not
*that* crazy :), so if there are any style mismatches... we'll have
to live with them for now.

app/widgets/gimpwindow.c

@@ -61,7 +61,7 @@ static gboolean  gimp_window_key_press_event (GtkWidget         *widget,
                                               GdkEventKey       *kevent);
 
 
-G_DEFINE_TYPE (GimpWindow, gimp_window, GTK_TYPE_WINDOW)
+G_DEFINE_TYPE_WITH_PRIVATE (GimpWindow, gimp_window, GTK_TYPE_WINDOW)
 
 #define parent_class gimp_window_parent_class
 
@@ -90,16 +90,12 @@ gimp_window_class_init (GimpWindowClass *klass)
   widget_class->screen_changed  = gimp_window_screen_changed;
   widget_class->configure_event = gimp_window_configure_event;
   widget_class->key_press_event = gimp_window_key_press_event;
-
-  g_type_class_add_private (klass, sizeof (GimpWindowPrivate));
 }
 
 static void
 gimp_window_init (GimpWindow *window)
 {
-  window->private = G_TYPE_INSTANCE_GET_PRIVATE (window,
-                                                 GIMP_TYPE_WINDOW,
-                                                 GimpWindowPrivate);
+  window->private = gimp_window_get_instance_private (window);
 
   window->private->monitor = -1;
 }