Add widget to call dispose, didChangeDependencies...

Hi, awesome package.

Can you add a widget to call functions like dispose, didChangeDependencies...

I've already implemented it if you want to use.
```dart
import 'package:flutter/material.dart';

class Stateful extends StatefulWidget {
final Widget child;
final Function initState;
final Function didChangeDependencies;
final Function dispose;

const Stateful({
Key key,
@required this.child,
this.dispose,
this.initState,
this.didChangeDependencies,
}) : super(key: key);

@override
_StatefulState createState() => _StatefulState();
}

class _StatefulState extends State {
@override
void initState() {
super.initState();
widget.initState?.call();
}

@override
void didChangeDependencies() {
super.didChangeDependencies();
widget.didChangeDependencies?.call();
}

@override
Widget build(BuildContext context) {
return widget.child;
}

@override
void dispose() {
widget.dispose?.call();
super.dispose();
}
}
```

I think we can join your current package with this new widget.
What do you think?