The identifier to use for state restoration of this app.
Providing a restoration ID inserts a RootRestorationScope into the widget hierarchy, which enables state restoration for descendant widgets.
Providing a restoration ID also enables the Navigator or Router built by the WidgetsApp to restore its state (i.e. to restore the history stack of active Routes). See the documentation on Navigator for more details around state restoration of Routes.
- RestorationManager, which explains how state restoration works in Flutter.
final String? restorationScopeId;