Create a way for users to try beta or master DevTools without having to switch their flutter version

Since we ship DevTools with the flutter SDK, we often run into a latency issue where we have shipped a DevTools version on Flutter master that has bug fixes users are interested in (e.g. the network page fixes of recent), but users have no way to try this DevTools version out unless they switch to the flutter master channel. This can be problematic for users, as they may not be able to switch to the master channel without a big lift.

We should design a way for users to try DevTools from Flutter Beta or Flutter master at the click of a button in DevTools. We will not be able to guarantee that this DevTools version will be compatible with the user's Flutter version, but we can warn users about this.

未指定任何文件、测试或入口点。首先追踪 DevTools 如何与 Flutter SDK 一起打包和选择，然后定义尝试 Beta 或 master 的用户流程以及兼容性警告。当用户无需更改 Flutter channel 即可选择这些 DevTools 版本时，即表示完成。

由索引模型根据 Issue 内容生成。