OnNavigationViewCreatedCallBack typedef
        OnNavigationViewCreatedCallBack =
     void Function(MapNavigationViewController controller)
    
    
Callback method for when the navigation view is ready to be used.
Pass to MapNavigationView.onMapCreated to receive a MapNavigationViewController when the
map is created.
Implementation
typedef OnNavigationViewCreatedCallBack = void Function(
    MapNavigationViewController controller);