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/gimpeditor.c

@@ -112,6 +112,7 @@ static void            gimp_editor_config_size_changed (GimpGuiConfig   *config,
 
 
 G_DEFINE_TYPE_WITH_CODE (GimpEditor, gimp_editor, GTK_TYPE_BOX,
+                         G_ADD_PRIVATE (GimpEditor)
                          G_IMPLEMENT_INTERFACE (GIMP_TYPE_DOCKED,
                                                 gimp_editor_docked_iface_init))
 
@@ -200,8 +201,6 @@ gimp_editor_class_init (GimpEditorClass *klass)
                                                               GTK_TYPE_RELIEF_STYLE,
                                                               DEFAULT_BUTTON_RELIEF,
                                                               GIMP_PARAM_READABLE));
-
-  g_type_class_add_private (klass, sizeof (GimpEditorPrivate));
 }
 
 static void
@@ -219,9 +218,7 @@ gimp_editor_init (GimpEditor *editor)
   gtk_orientable_set_orientation (GTK_ORIENTABLE (editor),
                                   GTK_ORIENTATION_VERTICAL);
 
-  editor->priv            = G_TYPE_INSTANCE_GET_PRIVATE (editor,
-                                                         GIMP_TYPE_EDITOR,
-                                                         GimpEditorPrivate);
+  editor->priv            = gimp_editor_get_instance_private (editor);
   editor->priv->popup_data      = editor;
   editor->priv->show_button_bar = TRUE;