一、背景

为了更好地支持将Flutter添加到现有项目的执行环境，旧的Android平台端包装器在io.flutter.app.FlutterActivity及其相关类托管Flutter运行时已被弃用。取而代之的则是io.flutter.embedding.android.FlutterActivity及其相关的类。如果我们不进行升级，那么运行flutter doctor命令时会报如下的错误。

Your Flutter application is created using an older version of the Android
embedding. It is being deprecated in favor of Android embedding v2. Follow the
steps at

https://flutter.dev/go/android-project-migration

to migrate your project. You may also pass the --ignore-deprecation flag to
ignore this check and continue with the deprecated v1 embedding. However,
the v1 Android embedding will be removed in future versions of Flutter.
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The detected reason was:

  No `/Users/mac/android/AndroidManifest.xml` file
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如果是纯Flutter工程，