Add callback for on modal dismiss with drag to be utilized in Navigator 2.0

[ulusoyca]

This PR adds onModalDismissedWithDrag field to the WoltModalSheetRoute to detect the modal dismiss with drag gesture.

When using imperative API, it is enough to call Navigator.of(context).pop() to dismiss the modal. In fact, this is the default behavior when dismiss callbacks are not provided by the library users. However, using Navigator 2.0 requires actions in the callbacks to update the app state that builds the navigation stack on modal dismiss events.

In this screen recording from navigator2 playground example, it can be seen that the address bar is updated with both barrier tap and dismiss by frag events.

Note that earlier, this was handled in router delegate with Navigator's onPop callback. We no longer need to handle this imperatively in the Navigator widget.

on_dismissed_with_drag.mov

[MuTe33]

Nice, like it! 🚢