安装flutter时，使用flutter doctor报错：
Android license status unknown.
Try re-installing or updating your Android SDK Manager.
See https://developer.android.com/studio/#downloads or visit https://flutter.dev/setup/#android-setup for detailed
instructions.
使用flutter doctor --android-licenses接着报错：
Android sdkmanager tool not found (D:AndroidSDK oolsbinsdkmanager).
Try re-installing or updating your Android SDK,
visit https://flutter.dev/setup/#android-setup for detailed instructions.
原因是Android SDK找不到tools目录。
根据网上办法，我下了SDK tools下所有文件，但仍然还是报那个问题。
发现我用的AS 3.6.1自动勾选了Hide Obsolete Packages，没有Android SDK Tools的下载目录。