iOS Flutter 2.10+ ~ 3.0.x 在Widget AutofillGroup组件存在时 pop页面发生crash

## Steps to Reproduce

`
@override
Widget build(BuildContext context) {
return SafeArea(
child: AutofillGroup(
child: Column(children: [
TextField(
autofillHints: [AutofillHints.email],
),
TextField(
autofillHints: [AutofillHints.password],
)
]),
));
}
`

1. 例如 Flutter版本 2.10.5下
2. 从一个原生页面跳转到刚包含AuotiFillGroup的页面
3. 返回到上一个页面 crash

**Flutter Boost Version** ref: v3.0-null-safety-release.2
**Target Platform:** iOS
**Target OS version/browser:** All versions
**Devices:** iPhone X

## Logs
`The application must have a host view since the keyboard client `

crash点在于 https://github.com/flutter/engine/blob/main/shell/platform/darwin/ios/framework/Source/FlutterTextInputPlugin.mm#L2337

```
[✓] Flutter (Channel stable, 3.0.1, on macOS 11.4 20F71 darwin-x64, locale en-CN)
• Flutter version 3.0.1 at /Users/user/fvm/versions/3.0.1
• Upstream repository https://github.com/flutter/flutter.git
• Framework revision fb57da5f94 (4 weeks ago), 2022-05-19 15:50:29 -0700
• Engine revision caaafc5604
• Dart version 2.17.1
• DevTools version 2.12.2
```

3.0.1也有一样的问题

Reproduce the iOS crash by navigating from a native page to a page containing AutofillGroup, then popping it. Start at FlutterTextInputPlugin.mm around line 2337 and verify that returning from the AutofillGroup page no longer crashes with Flutter 2.10–3.0.x; no test file is named.

Written by the indexing model from the issue text.