app: port GimpDrawableUndo, GimpDrawable::push_undo() and ::swap_tiles()

which gets rid of the manual implementation of sparse undo buffers,
but GEGL will take care of proper COW here soo enough.

app/core/gimpdrawable-combine.c

@@ -101,9 +101,9 @@ gimp_drawable_real_apply_region (GimpDrawable         *drawable,
       GimpDrawableUndo *undo;
 
       gimp_drawable_push_undo (drawable, undo_desc,
+                               NULL,
                                x1, y1,
-                               x2 - x1, y2 - y1,
-                               NULL, FALSE);
+                               x2 - x1, y2 - y1);
 
       undo = GIMP_DRAWABLE_UNDO (gimp_image_undo_get_fadeable (image));
 
@@ -258,9 +258,9 @@ gimp_drawable_real_replace_region (GimpDrawable *drawable,
   /*  If the calling procedure specified an undo step...  */
   if (push_undo)
     gimp_drawable_push_undo (drawable, undo_desc,
+                             NULL,
                              x1, y1,
-                             x2 - x1, y2 - y1,
-                             NULL, FALSE);
+                             x2 - x1, y2 - y1);
 
   /* configure the pixel regions */
   pixel_region_init (&src1PR, gimp_drawable_get_tiles (drawable),