Handle requires `Scrollable` being present in the widget tree after upgrade to Flutter 3.7

[ukasz123]

Flutter 3.7 introduced change to the behavior of Scrollable.of - it requires the Scrollable being present in the parent tree and returns non-nullable value.

This makes some uses of Handle widget to crash when accessing parent Scrollable (here). The simple solution is to replace Scrollable.of with Scrollable.maybeOf.

Minimal code reproducing the issue

import 'package:flutter/material.dart';
import 'package:implicitly_animated_reorderable_list_2/implicitly_animated_reorderable_list_2.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      title: 'Flutter Demo',
      home: DemoPage(),
    );
  }
}

class DemoPage extends StatefulWidget {
  const DemoPage({super.key});

  @override
  State<DemoPage> createState() => _DemoPageState();
}

class _DemoPageState extends State<DemoPage> {
  var items = List.generate(15, (index) => "Index $index");

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: ImplicitlyAnimatedReorderableList(
        items: items,
        itemBuilder: (context, animation, item, index) => Reorderable(
          key: ValueKey(item),
          builder: (context, _, __) => ListTile(
            leading: const Handle(
                child: Padding(
              padding: EdgeInsets.all(8),
              child: Icon(Icons.drag_handle_outlined),
            )),
            title: Text(item),
          ),
        ),
        areItemsTheSame: (l, r) => l == r,
        onReorderFinished:
            (String item, int from, int to, List<String> newItems) {
          setState(() {
            items = newItems;
          });
        },
      ),
    );
  }
}