routeNameMappingsContains method
Checks if the route name mappings contain a route name.
Implementation
bool routeNameMappingsContains(String name) {
  bool routeNamedArg = isRouteNamedArg(name);
  if (routeNamedArg) {
    return true;
  }
  return _routeNameMappings.containsKey(name);
}