設定方法
パッケージflutter_launcher_icons を利用する
pubspec.yaml iOS, Androidアプリの設定
dev_dependencies:
flutter_launcher_icons: ^0.12.0
flutter_icons:
android: "launcher_icon"
ios: true
image_path: "assets/icon/icon.png"
min_sdk_android: 21 # android min sdk min:16, default 21