Keyboard not showing up in iOS

## System info

Issue occurs on: iOS
Plugin version: 0.3.11
Flutter doctor output:

```
Doctor summary (to see all details, run flutter doctor -v):
[✓] Flutter (Channel stable, 1.22.4, on macOS 11.0.1 20B29 darwin-x64, locale en-IN)

[✓] Android toolchain - develop for Android devices (Android SDK version 29.0.3)
[✓] Xcode - develop for iOS and macOS (Xcode 12.2)
[!] Android Studio (version 4.1)
✗ Flutter plugin not installed; this adds Flutter specific functionality.
✗ Dart plugin not installed; this adds Dart specific functionality.

[✓] Connected device (1 available)

! Doctor found issues in 1 category.
```

## Steps to Reproduce

Please see my [code here](https://gist.github.com/ash007osh/4694a290edb5a6603b65c655c4da5002)

## Logs

```
Nothing related to this particular page
```

Unrelated Issues:
```
info • 'title' is deprecated and shouldn't be used. Use "label" instead, as it allows for an improved text-scaling
experience. This feature was deprecated after v1.19.0. • lib/navbar.dart:11:13 • deprecated_member_use
info • 'title' is deprecated and shouldn't be used. Use "label" instead, as it allows for an improved text-scaling
experience. This feature was deprecated after v1.19.0. • lib/navbar.dart:15:13 • deprecated_member_use
info • 'title' is deprecated and shouldn't be used. Use "label" instead, as it allows for an improved text-scaling
experience. This feature was deprecated after v1.19.0. • lib/navbar.dart:19:13 • deprecated_member_use

3 issues found. (ran in 116.9s)
```

```
[✓] Flutter (Channel stable, 1.22.4, on macOS 11.0.1 20B29 darwin-x64, locale en-IN)
• Flutter version 1.22.4 at /Users/innovationswork/Desktop/flutter
• Framework revision 1aafb3a8b9 (9 days ago), 2020-11-13 09:59:28 -0800
• Engine revision 2c956a31c0
• Dart version 2.10.4

[✓] Android toolchain - develop for Android devices (Android SDK version 29.0.3)
• Android SDK at /Users/innovationswork/Library/Android/sdk
• Platform android-29, build-tools 29.0.3
• Java binary at: /Applications/Android Studio.app/Contents/jre/jdk/Contents/Home/bin/java
• Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b3-6915495)
• All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS (Xcode 12.2)
• Xcode at /Applications/Xcode.app/Contents/Developer
• Xcode 12.2, Build version 12B45b
• CocoaPods version 1.9.3

[!] Android Studio (version 4.1)
• Android Studio at /Applications/Android Studio.app/Contents
✗ Flutter plugin not installed; this adds Flutter specific functionality.
✗ Dart plugin not installed; this adds Dart specific functionality.
• Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b3-6915495)

[✓] Connected device (1 available)
• iPhone SE (2nd generation) (mobile) • 0D3AA587-7F8B-475F-8C6F-5F8EE5F505EA • ios •
com.apple.CoreSimulator.SimRuntime.iOS-14-2 (simulator)

! Doctor found issues in 1 category.```

Bắt đầu bằng cách tái hiện gist được liên kết trên iOS với flutter_webview_plugin 0.3.11, Flutter 1.22.4 và iOS 14.2, sau đó kiểm tra hành vi của bàn phím iOS và WebView của plugin. Được xem là hoàn tất khi bàn phím phần mềm xuất hiện lúc một ô nhập liệu trong WebView nhận focus; issue không xác định tệp nào trong repository hoặc bài kiểm thử nào.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.