app: start porting away from GtkAction and friends

Step one: get rid of all those deprecation warnings that make
it hard to see any other warnings:

- add a lot of dummy API to GimpAction, GimpActionGroup, GimpUIManager
  etc. which simply forwards to the deprecated GTK functions, they
  will all go away again later
- rename GimpAction to GimpActionImpl
- add interface GimpAction that is implemented by all action classes,
  creates a common interface and allows to remove some duplicated
  logic from GimpToggleAction and GimpRadioAction, and at the same
  time adds more features

(cherry picked from commit 86e07c16b5)

Merged to gimp-2-10 to keep the diff to master as small as possible

app/actions/data-editor-commands.c

@@ -23,6 +23,7 @@
 #include "actions-types.h"
 
 #include "widgets/gimpdataeditor.h"
+#include "widgets/gimptoggleaction.h"
 
 #include "data-editor-commands.h"
 
@@ -36,7 +37,7 @@ data_editor_edit_active_cmd_callback (GtkAction *action,
   GimpDataEditor *editor = GIMP_DATA_EDITOR (data);
   gboolean        edit_active;
 
-  edit_active = gtk_toggle_action_get_active (GTK_TOGGLE_ACTION (action));
+  edit_active = gimp_toggle_action_get_active (GIMP_TOGGLE_ACTION (action));
 
   gimp_data_editor_set_edit_active (editor, edit_active);
 }