Provides an opaque handle to the calculated Route. A handle encodes the calculated route. The route can be decoded from a handle at a later point in time as long as the service uses the same map data which was used during encoding. Note that the Route.getRouteHandle() is provided only if RouteOptions.enableRouteHandle is set before route calculation. A RouteHandle generated by the online RoutingEngine is not compatible with the OfflineRoutingEngine. Similarly, a RouteHandle from the OfflineRoutingEngine cannot be used with the online RoutingEngine. Using an incompatible RouteHandle results in a RoutingError.