function SwitchObservable(source) {
      this.source = source;
      __super__.call(this);
    }
Returns the values from the source observable sequence only after the other observable sequence produces a value.
@param {Observable | Promise} other The observable sequence or Promise that triggers propagation of elements of the source sequence.
@returns {Observable} An observable sequence containing the elements of the source sequence starting from the point the other sequence triggered propagation.