T, R> constructor Null safety
Constructs a Stream that observes an Iterable of Stream
and builds a List containing all latest events emitted by the provided Iterable of Stream.
combiner maps this List into a new event of type
CombineLatestStream( Iterable<Stream<T>> streams, R Function(List<T> values) combiner, ) : super(_buildController(streams, combiner).stream);