message: Add utility method to build a vector of struct in-place.
diff: @@ -1128,6 +1128,27 @@ FLATBUFFERS_FINAL_CLASS
  return Offset<Vector<const T *>>(EndVector(len));
  }
  + #ifndef FLATBUFFERS_CPP98_STL
  + /// @brief Serialize an array of structs into a FlatBuffer `vector`.
  + /// @tparam T The data type of the struct array elements.
  + /// @param[in] f A function that takes the current iteration 0..vector_size-1
  + /// and a pointer to the struct that must be filled.
  + /// @return Returns a typed `Offset` into the serialized data indicating
  + /// where the vector is stored.
  + /// This is mostly useful when flatbuffers are generated with mutation
  + /// accessors.
  + template<typename T> Offset<Vector<const T *>> CreateVectorOfStructs(
  + size_t vector_size, const std::function<void(size_t i, T *)> &filler) {
  + StartVector(vector_size * sizeof(T) / AlignOf<T>(), AlignOf<T>());
  + T *structs = reinterpret_cast<T *>(buf_.make_space(vector_size * sizeof(T)));
  + for (size_t i = 0; i < vector_size; i++) {
  + filler(i, structs);
  + structs++;
  + }
  + return Offset<Vector<const T *>>(EndVector(vector_size));
  + }
  + #endif
  +
  /// @brief Serialize a `std::vector` of structs into a FlatBuffer `vector`.
  /// @tparam T The data type of the `std::vector` struct elements.
  /// @param[in]] v A const reference to the `std::vector` of structs to
  