Popping the last page of the flow should complete the flow

Is your feature request related to a problem? Please describe. Since using Navigator.pop() goes back in the flow, it would be nice if this remains consistent even when the flow only has one page. I would expect popping the last page to complete the flow.

Having the above functionality makes nesting FlowBuilders very convenient.

Example

```dart import 'package:flow_builder/flow_builder.dart'; import 'package:flutter/material.dart'; void main() { runApp(const MaterialApp(home: _HomeFlow())); } enum _HomeFlowState { home, settings, } class _HomeFlow extends StatelessWidget { const _HomeFlow({Key? key}) : super(key: key); static List _onGeneratePages(_HomeFlowState state, List pages) { switch (state) { case _HomeFlowState.home: return [_HomePage.page()]; case _HomeFlowState.settings: return [_HomePage.page(), _SettingsFlow.page()]; } } @override Widget build(BuildContext context) { return const FlowBuilder( state: _HomeFlowState.home, onGeneratePages: _onGeneratePages, ); } } class _HomePage extends StatelessWidget { const _HomePage({Key? key}) : super(key: key); static Page page() => const MaterialPage(child: _HomePage()); @override Widget build(BuildContext context) { return Scaffold( appBar: AppBar( actions: [ IconButton( onPressed: () => context .flow<_HomeFlowState>() .update((_) => _HomeFlowState.settings), icon: const Icon(Icons.settings), ), ], ), body: const Center(child: Text('home')), ); } } enum _SettingsFlowState { settings, about, support, } class _SettingsFlow extends StatelessWidget { const _SettingsFlow({Key? key}) : super(key: key); static Page page() => const MaterialPage(child: _SettingsFlow()); static List _onGeneratePages( _SettingsFlowState state, List pages) { switch (state) { case _SettingsFlowState.settings: return [_SettingsPage.page()]; case _SettingsFlowState.about: return [_SettingsPage.page(), _AboutPage.page()]; case _SettingsFlowState.support: return [_SettingsPage.page(), _SupportPage.page()]; } } @override Widget build(BuildContext context) { return const FlowBuilder( state: _SettingsFlowState.settings, onGeneratePages: _onGeneratePages, ); } } class _SettingsPage extends StatelessWidget { const _SettingsPage({Key? key}) : super(key: key); static Page page() => const MaterialPage(child: _SettingsPage()); @override Widget build(BuildContext context) { // Native pop should also complete the flow. return Scaffold( appBar: AppBar( leading: BackButton(onPressed: () => Navigator.of(context).pop()), // Should complete the flow title: const Text('Settings'), ), body: Center( child: Column( children: [ TextButton( onPressed: () => context .flow<_SettingsFlowState>() .update((_) => _SettingsFlowState.about), child: const Text('About'), ), TextButton( onPressed: () => context .flow<_SettingsFlowState>() .update((_) => _SettingsFlowState.support), child: const Text('Support'), ), ], ), ), ); } } class _AboutPage extends StatelessWidget { const _AboutPage({Key? key}) : super(key: key); static Page page() => const MaterialPage(child: _AboutPage()); @override Widget build(BuildContext context) { return Scaffold( appBar: AppBar(title: const Text('About')), body: const Center(child: Text('About')), ); } } class _SupportPage extends StatelessWidget { const _SupportPage({Key? key}) : super(key: key); static Page page() => const MaterialPage(child: _SupportPage()); @override Widget build(BuildContext context) { return Scaffold( appBar: AppBar(title: const Text('Support')), body: const Center(child: Text('Support')), ); } } ```

Describe the solution you'd like I would like to have some logic that makes the flow complete whenever the last page of the flow is popped.

Describe alternatives you've considered N/A

Additional context N/A

felangel / flow_builder

Popping the last page of the flow should complete the flow #104