Create a function that splits a string into an array of identical clusters.
splitGroups("555") β ["555"]
splitGroups("5556667788") β ["555", "666", "77", "88"]
splitGroups("aaabbbaabbab") β ["aaa", "bbb", "aa", "bb", "a", "b"]
splitGroups("abbbcc88999&&!!!_") β ["a", "bbb", "cc", "88", "999", "&&", "!!!", "_"]