combine4<A, B, C, D, R>  static method 
Constructs a CombineLatestStream from 4 Streams
where combiner is used to create a new event of type R, based on the
latest events emitted by the provided Streams.
Implementation
static CombineLatestStream<dynamic, R> combine4<A, B, C, D, R>(
  Stream<A> streamA,
  Stream<B> streamB,
  Stream<C> streamC,
  Stream<D> streamD,
  R Function(A a, B b, C c, D d) combiner,
) =>
    CombineLatestStream<dynamic, R>(
      [streamA, streamB, streamC, streamD],
      (List<dynamic> values) {
        return combiner(
          values[0] as A,
          values[1] as B,
          values[2] as C,
          values[3] as D,
        );
      },
    );