Repository: flutter
Issue: [IOS] Keyboard opens unexpectedly when navigating back to page with textfield.
Labels: a: text input,platform-ios,framework,f: routes,f: focus,has reproducible steps,P2,found in release: 2.8,found in release: 2.9,team-ios,triaged-ios

## Steps to Reproduce

1. Create a new project (Flutter 2.5.0)
2. Create a new file second_page.dart
3. Paste code sample to main.dart and second_page.dart
4. Run on iPhone (only on iOS)
5. Tap the textfield in `MyHomePage`
6. Tap `Open Second Page`
7. Tap `Open Next Page`
8. Tap back button or swipe back to `Second Page`

Keyboard will open on `Second Page` after step 8, the `_focusNode` become `primaryFocus`.

**Expected results:** Keyboard opens when I swipe back to `MyHomePage`

**Actual results:** <!-- what did you see? -->

https://user-images.githubusercontent.com/3602624/147027078-0e21752a-1203-45d2-8505-0e98410df049.MP4

## Code sample
### main.dart
```dart
import 'package:flutter/material.dart';
import 'package:flutter_app/second_page.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({Key? key, required this.title}) : super(key: key);

  final String title;

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {

  final _controller = TextEditingController();
  final _focusNode = FocusNode();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Column(
        children: [
          TextField(
            controller: _controller,
            focusNode: _focusNode,
          ),
          GestureDetector(
            onTap: _openSecondPage,
            child: Container(
                height: 56,
                decoration: BoxDecoration(),
                child: Text('Open Second Page')
            ),
          )
        ],
      ),
    );
  }

  void _openSecondPage() {
    Navigator.of(context).push(MaterialPageRoute(builder: (context) {
      return SecondPage(title: 'Second Page');
    }));
  }
}
```
### second_page.dart
```dart
import 'package:flutter/material.dart';

class SecondPage extends StatefulWidget {
  final String title;

  SecondPage({required this.title});

  @override
  _SecondPageState createState() => _SecondPageState();
}

class _SecondPageState extends State<SecondPage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: GestureDetector(
          onTap: _openNextPage,
          child: Container(
              height: 56,
              decoration: BoxDecoration(),
              child: Text('Open Next Page')
          ),
        ),
      ),
    );
  }

  void _openNextPage() {
    Navigator.of(context).push(MaterialPageRoute(builder: (context) {
      return SecondPage(title: 'Next page');
    }));
  }
}
```