33. implement TupleToString<T>

Implement TupleToString<T> to return a new type by concatenating all the string to a new string type.

type A = TupleToString<['a']> // 'a'
type B = TupleToString<['B', 'F', 'E']> // 'BFE'
type C = TupleToString<[]> // ''