message: Add new mutable tuple_elements accessor to HloSharding
diff: @@ -207,6 +207,7 @@ class HloSharding {
  // Returns the flattened list of all the leaf shardings in a tuple shape, by
  // pre-order walk (ShapeTree iterator order).
  // REQUIRES: IsTuple().
  + std::vector<HloSharding>& tuple_elements() { return tuple_elements_; }
  const std::vector<HloSharding>& tuple_elements() const {
  return tuple_elements_;
  }
  