Function swap_where_both_have_value

test-app/runtime/src/main/cpp/ada/ada.h:3515–3517

  using move_constructing_e_can_throw = std::false_type;

  void swap_where_both_have_value(expected & /*rhs*/, t_is_void) noexcept {
    // swapping void is a no-op
  }

  void swap_where_both_have_value(expected &rhs, t_is_not_void) {
    using std::swap;