runtimeType property
This is a hack to save it and find it with the id distinction
in _inheritedWidgets of Element using the helper functions
of BuildContext like getElementForInheritedWidgetOfExactType.
Implementation
@override
Type get runtimeType {
Type getType<TT>() => TT;
if (id != null) {
return getType<_ReactterProviderKey<T, String>>();
}
return getType<_ReactterProviderKey<T, Null>>();
}