Support accessibility back gesture to pop route from view controller

[jmagman]

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Adapted suggestion from https://github.com/flutter/flutter/issues/74246#issuecomment-971326926 to pop the route if the view controller route if accessibilityPerformEscape is called at that level in the responder chain.

Ideally this could know if the route was successfully popped, and only then return YES (halting propagation through the responder chain).

I confirmed by editing https://docs.flutter.dev/cookbook/navigation/navigation-basics#interactive-example as a demo that that the two-finger scrub (move two fingers back and forth three times quickly, making a "z") navigates back to the last route, and that the SementicObject scrub, which already worked, continued to work.

I'm not super familiar with this code, hopefully there aren't further gotchas I'm not thinking of.

Fixes https://github.com/flutter/flutter/issues/74246

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[jmagman]

@hangyujin are you the best person to review this since @chunhtai is out? Or should I add someone else?

[vashworth]

Did you also try dismissing a dialog (example: https://api.flutter.dev/flutter/material/showDialog.html)? Seems to me it should probably work too

[jmagman]

Did you also try dismissing a dialog (example: https://api.flutter.dev/flutter/material/showDialog.html)? Seems to me it should probably work too

Confirmed that worked on main and also on this branch.

[jmagman]

Routes and modal combined, showing the modal is dismissed before the route is popped

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

void main() {
  runApp(const MaterialApp(
    title: 'Navigation Basics',
    home: FirstRoute(),
  ));
}

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

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('First Route'),
      ),
      body: Center(
        child: ElevatedButton(
          child: const Text('Open route'),
          onPressed: () {
            Navigator.push(
              context,
              MaterialPageRoute(builder: (context) => const SecondRoute()),
            );
          },
        ),
      ),
    );
  }
}

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

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Second Route'),
      ),
      body: Center(
        child: ElevatedButton(
          onPressed: () {
            Navigator.of(context).restorablePush(_modalBuilder);
          },
          child: const Text('Open Modal'),
        ),
      ),
    );
  }

  @pragma('vm:entry-point')
  static Route<void> _modalBuilder(BuildContext context, Object? arguments) {
    return CupertinoModalPopupRoute<void>(
      builder: (BuildContext context) {
        return CupertinoActionSheet(
          title: const Text('Title'),
          message: const Text('Message'),
          actions: <CupertinoActionSheetAction>[
            CupertinoActionSheetAction(
              child: const Text('Action One'),
              onPressed: () {
                Navigator.pop(context);
              },
            ),
            CupertinoActionSheetAction(
              child: const Text('Action Two'),
              onPressed: () {
                Navigator.pop(context);
              },
            ),
          ],
        );
      },
    );
  }
}

(gesture done at :09 and :13) https://github.com/flutter/engine/assets/682784/8886cd6e-ab0d-4258-8015-f0dd0ed7329c