Write a method called symmetricSetDifference that accepts two Sets as parameters and returns a new Set containing their symmetric set difference (that is, the set of elements contained in either of the two sets but not in both). For example, the symmetric difference between the sets [1, 4, 7, 9] and [2, 4, 5, 6, 7] is [1, 2, 5, 6, 9].