Este método deve ser utilizado quando for necessário alterar a ordem entre os valores TLeft e TRight.
Either<string, int> either = 42;
Either<int, string> eitherResult = either.Swap();
//eitherResult.IsLeft = true
//eitherResult.Left = 42
Either<string, int> either = "Hello";
Either<int, string> eitherResult = either.Swap();
//eitherResult.IsRight = true
//eitherResult.Right = "Hello"