The plugin `flutter_webview_plugin` uses a deprecated version of the Android embedding

## System info

Issue occurs on: both
Plugin version: 0.4.0
Flutter doctor output:

```
$ flutter doctor -v
[✓] Flutter (Channel stable, 2.5.0, on macOS 11.5.2 20G95 darwin-x64,
locale en-GB)
• Flutter version 2.5.0 at /Users/andre.paraense/Projects/flutter
• Upstream repository https://github.com/flutter/flutter.git
• Framework revision 4cc385b4b8 (5 days ago), 2021-09-07 23:01:49
-0700
• Engine revision f0826da7ef
• Dart version 2.14.0

[✓] Android toolchain - develop for Android devices (Android SDK
version 30.0.0-rc2)
• Android SDK at /Users/andre.paraense/Library/Android/sdk
• Platform android-30, build-tools 30.0.0-rc2
• ANDROID_HOME = /Users/andre.paraense/Library/Android
• Java binary at: /Applications/Android
Studio.app/Contents/jre/Contents/Home/bin/java
• Java version OpenJDK Runtime Environment (build
11.0.10+0-b96-7281165)
• All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS
• Xcode at /Applications/Xcode.app/Contents/Developer
• Xcode 12.5.1, Build version 12E507
• CocoaPods version 1.11.1

[✓] Chrome - develop for the web
• Chrome at /Applications/Google Chrome.app/Contents/MacOS/Google
Chrome

[✓] Android Studio (version 2020.3)
• Android Studio at /Applications/Android Studio.app/Contents
• Flutter plugin can be installed from:
🔨 https://plugins.jetbrains.com/plugin/9212-flutter
• Dart plugin can be installed from:
🔨 https://plugins.jetbrains.com/plugin/6351-dart
• Java version OpenJDK Runtime Environment (build
11.0.10+0-b96-7281165)

[✓] VS Code (version 1.60.0)
• VS Code at /Applications/Visual Studio Code.app/Contents
• Flutter extension can be installed from:
🔨
https://marketplace.visualstudio.com/items?itemName=Dart-Code.flu
tter

[✓] Connected device (3 available)
• sdk gphone x86 (mobile) • emulator-5554
• android-x86 • Android 11 (API 30) (emulator)
• iPhone 12 Pro Max (mobile) • C86AC201-D1ED-41A5-ADBA-A2F609200150
• ios • com.apple.CoreSimulator.SimRuntime.iOS-14-5
(simulator)
• Chrome (web) • chrome
• web-javascript • Google Chrome 93.0.4577.63

• No issues found!

```

## Steps to Reproduce

Just run any application using `flutter_webview_plugin` version `0.4.0` after upgrading to Flutter 2.5 and you will get the warning message.

## Logs

```
The plugin `flutter_webview_plugin` uses a deprecated version of the
Android embedding.
To avoid unexpected runtime failures, or future build failures, try to see
if this plugin supports the Android V2 embedding. Otherwise, consider
removing it since a future release of Flutter will remove these deprecated
APIs.
If you are plugin author, take a look at the docs for migrating the plugin
to the V2 embedding: https://flutter.dev/go/android-plugin-migration.
```

Inizia con la guida alla migrazione del plugin Android collegata nell’issue, quindi esamina l’implementazione Android del plugin per determinare a cosa si riferisce l’avviso relativo a deprecated embedding. Riproduci l’avviso con Flutter 2.5 e un’applicazione che utilizza la versione 0.4.0; il lavoro è completato quando l’avviso non compare più e il plugin continua a funzionare.

Scritto dal modello di indicizzazione a partire dal testo della issue.