make `Container` node aware of `Size Flags`

scene/gui/container.cpp

@@ -151,6 +151,18 @@ void Container::_notification(int p_what) {
 				queue_sort();
 			}
 		} break;
+		case NOTIFICATION_SORT_CHILDREN: {
+
+			Size2 s = get_size();
+
+			for (int i=0; i<get_child_count();i++) {
+				Control *c = get_child(i)->cast_to<Control>();
+				if (!c || !c->is_visible() || c->is_set_as_toplevel())
+					continue;
+
+				fit_child_in_rect(c,Rect2(0, 0, s.width, s.height));
+			}
+		}
 	}
 }