Leverage DraggableScrollabeController Once It's Available

[caseycrogers]

When #149 goes in, developers using the expandable bottom sheet feature will have to use FeedbackSheetDragHandle in the feedback sheet builder to provide a visual drag handle for users.

This is pretty clunky, but the only way to do it because the drag handle needs to be placed as a fixed header on top of their scrollable widget in order for users to be able to click and drag on it to drag the sheet. Once DraggableScrollableSheet supports programmatic control in production (see: flutter/flutter#92440) we can pull the drag handle out of the builder so that developers don't have to provide it.

Additionally, the feedback_widget uses a value notifier internally to manage sheet related animations. This can also be replaced by referencing the controller directly assuming the controller is made a ChangeNotifier.

[kamami]

Any updates to this?

[ueman]

DraggableScrollabeController will probably be included in the next Flutter version. There's no date for that yet, but I expect it to be around February or March.

[kamami]

Is already on master and fully functional?

[ueman]

I'm not sure what you're referring to. flutter/flutter#92440 is already on master and fully functional. This library however doesn't yet support it.

[kamami]

Thanks for your response! I missed that this is a separate package...

[quoc-huynh-cosee]

Any updates on this? I need to expand the sheet programatically.

[ueman]

Closed via #239