docs: public ViewTransitionBuilder transitViewGroup(@NonNull ViewGroupTransition viewGroupTransition) {
          ViewGroup vg = (ViewGroup) mView;
          int total = vg.getChildCount();
          View view;
          ViewGroupTransitionConfig config = new ViewGroupTransitionConfig(vg, total);
          for (int i = 0; i < total; i++) {
              view = vg.getChildAt(i);
              config.childView = view;
              config.index = i;
              viewGroupTransition.transit(target(view), config);
          }
          return self();
      }