Flatten a nested array
You must account for varying levels of nesting

steamrollArray([[["a"]], [["b"]]]) should return ["a", "b"]

steamrollArray([1, [2], [3, [[4]]]]) should return [1, 2, 3, 4]

steamrollArray([1, [], [3, [[4]]]]) should return [1, 3, 4]

steamrollArray([1, {}, [3, [[4]]]]) should return [1, {}, 3, 4]

Your solution should not use the Array.prototype.flat() or Array.prototype.flatMap() methods

Global variables should not be used