app: GtkAction -> GAction madness part two

Change all action callbacks so they can be invoked by a GAction:

- add GimpActionCallback typedef:
  void (* cb) (GimpAction*, GVariant*, gpointer)
- change all action callbacks to the GimpActionCallback signature
- add "gimp-activate" and "gimp-change-state" signals to GimpAction,
  with the same signature as the resp. GAction signals
- remove all other custom action signals and only use the new
  GimpAction signals
- pass around appropriate GVariants containing booleans, int32,
  strings
- badly hack around to force a GimpProcedure pointer into a
  uint64 variant
- remove all G_CALLBACK() casts from all action callbacks,
  they all have the same signature now

(cherry picked from commit 3b6b3fc189)

app/actions/edit-actions.c

@@ -73,93 +73,93 @@ static const GimpActionEntry edit_actions[] =
   { "edit-undo", GIMP_ICON_EDIT_UNDO,
     NC_("edit-action", "_Undo"), "<primary>Z",
     NC_("edit-action", "Undo the last operation"),
-    G_CALLBACK (edit_undo_cmd_callback),
+    edit_undo_cmd_callback,
     GIMP_HELP_EDIT_UNDO },
 
   { "edit-redo", GIMP_ICON_EDIT_REDO,
     NC_("edit-action", "_Redo"), "<primary>Y",
     NC_("edit-action", "Redo the last operation that was undone"),
-    G_CALLBACK (edit_redo_cmd_callback),
+    edit_redo_cmd_callback,
     GIMP_HELP_EDIT_REDO },
 
   { "edit-strong-undo", GIMP_ICON_EDIT_UNDO,
     NC_("edit-action", "Strong Undo"), "<primary><shift>Z",
     NC_("edit-action", "Undo the last operation, skipping visibility changes"),
-    G_CALLBACK (edit_strong_undo_cmd_callback),
+    edit_strong_undo_cmd_callback,
     GIMP_HELP_EDIT_STRONG_UNDO },
 
   { "edit-strong-redo", GIMP_ICON_EDIT_REDO,
     NC_("edit-action", "Strong Redo"), "<primary><shift>Y",
     NC_("edit-action",
         "Redo the last operation that was undone, skipping visibility changes"),
-    G_CALLBACK (edit_strong_redo_cmd_callback),
+    edit_strong_redo_cmd_callback,
     GIMP_HELP_EDIT_STRONG_REDO },
 
   { "edit-undo-clear", GIMP_ICON_SHRED,
     NC_("edit-action", "_Clear Undo History"), NULL,
     NC_("edit-action", "Remove all operations from the undo history"),
-    G_CALLBACK (edit_undo_clear_cmd_callback),
+    edit_undo_clear_cmd_callback,
     GIMP_HELP_EDIT_UNDO_CLEAR },
 
   { "edit-cut", GIMP_ICON_EDIT_CUT,
     NC_("edit-action", "Cu_t"), "<primary>X",
     NC_("edit-action", "Move the selected pixels to the clipboard"),
-    G_CALLBACK (edit_cut_cmd_callback),
+    edit_cut_cmd_callback,
     GIMP_HELP_EDIT_CUT },
 
   { "edit-copy", GIMP_ICON_EDIT_COPY,
     NC_("edit-action", "_Copy"), "<primary>C",
     NC_("edit-action", "Copy the selected pixels to the clipboard"),
-    G_CALLBACK (edit_copy_cmd_callback),
+    edit_copy_cmd_callback,
     GIMP_HELP_EDIT_COPY },
 
   { "edit-copy-visible", NULL, /* GIMP_ICON_COPY_VISIBLE, */
     NC_("edit-action", "Copy _Visible"), "<primary><shift>C",
     NC_("edit-action", "Copy what is visible in the selected region"),
-    G_CALLBACK (edit_copy_visible_cmd_callback),
+    edit_copy_visible_cmd_callback,
     GIMP_HELP_EDIT_COPY_VISIBLE },
 
   { "edit-paste-as-new-image", GIMP_ICON_EDIT_PASTE_AS_NEW,
     NC_("edit-action", "From _Clipboard"), "<primary><shift>V",
     NC_("edit-action", "Create a new image from the content of the clipboard"),
-    G_CALLBACK (edit_paste_as_new_image_cmd_callback),
+    edit_paste_as_new_image_cmd_callback,
     GIMP_HELP_EDIT_PASTE_AS_NEW_IMAGE },
 
   { "edit-paste-as-new-image-short", GIMP_ICON_EDIT_PASTE_AS_NEW,
     NC_("edit-action", "_New Image"), NULL,
     NC_("edit-action", "Create a new image from the content of the clipboard"),
-    G_CALLBACK (edit_paste_as_new_image_cmd_callback),
+    edit_paste_as_new_image_cmd_callback,
     GIMP_HELP_EDIT_PASTE_AS_NEW_IMAGE },
 
   { "edit-named-cut", GIMP_ICON_EDIT_CUT,
     NC_("edit-action", "Cu_t Named..."), NULL,
     NC_("edit-action", "Move the selected pixels to a named buffer"),
-    G_CALLBACK (edit_named_cut_cmd_callback),
+    edit_named_cut_cmd_callback,
     GIMP_HELP_BUFFER_CUT },
 
   { "edit-named-copy", GIMP_ICON_EDIT_COPY,
     NC_("edit-action", "_Copy Named..."), NULL,
     NC_("edit-action", "Copy the selected pixels to a named buffer"),
-    G_CALLBACK (edit_named_copy_cmd_callback),
+    edit_named_copy_cmd_callback,
     GIMP_HELP_BUFFER_COPY },
 
   { "edit-named-copy-visible", NULL, /* GIMP_ICON_COPY_VISIBLE, */
     NC_("edit-action", "Copy _Visible Named..."), "",
     NC_("edit-action",
         "Copy what is visible in the selected region to a named buffer"),
-    G_CALLBACK (edit_named_copy_visible_cmd_callback),
+    edit_named_copy_visible_cmd_callback,
     GIMP_HELP_BUFFER_COPY },
 
   { "edit-named-paste", GIMP_ICON_EDIT_PASTE,
     NC_("edit-action", "_Paste Named..."), NULL,
     NC_("edit-action", "Paste the content of a named buffer"),
-    G_CALLBACK (edit_named_paste_cmd_callback),
+    edit_named_paste_cmd_callback,
     GIMP_HELP_BUFFER_PASTE },
 
   { "edit-clear", GIMP_ICON_EDIT_CLEAR,
     NC_("edit-action", "Cl_ear"), "Delete",
     NC_("edit-action", "Clear the selected pixels"),
-    G_CALLBACK (edit_clear_cmd_callback),
+    edit_clear_cmd_callback,
     GIMP_HELP_EDIT_CLEAR }
 };
 
@@ -245,12 +245,12 @@ edit_actions_setup (GimpActionGroup *group)
   gimp_action_group_add_enum_actions (group, "edit-action",
                                       edit_paste_actions,
                                       G_N_ELEMENTS (edit_paste_actions),
-                                      G_CALLBACK (edit_paste_cmd_callback));
+                                      edit_paste_cmd_callback);
 
   gimp_action_group_add_enum_actions (group, "edit-action",
                                       edit_fill_actions,
                                       G_N_ELEMENTS (edit_fill_actions),
-                                      G_CALLBACK (edit_fill_cmd_callback));
+                                      edit_fill_cmd_callback);
 
   action = gimp_action_group_get_action (group,
                                          "edit-paste-as-new-image-short");