Method init_by_copying

cpp/src/arrow/util/small_vector.h:462–468

 private:
  template <typename InputIt>
  void init_by_copying(size_t n, InputIt src) {
    storage_.bump_size(n);
    auto* dest = storage_.storage_ptr();
    for (size_t i = 0; i < n; ++i, ++src) {
      dest[i].construct(*src);
    }
  }

  template <typename InputIt>
  void init_by_moving(size_t n, InputIt src) {