Refactor launch_url and copy_to_clipboard

See original discussion here:
https://github.com/flutter/devtools/pull/6598#discussion_r1373364646

both essentially use postMessage, so if we created a config_specific implementation of postmessage, then they could use that instead of both creating a bunch of stub files.

首先阅读链接的讨论，并定位 launch_url、copy_to_clipboard 及其对 postMessage 的使用。只有当两者都使用特定于配置的 postMessage 实现，而不是创建单独的 stub 文件时，重构才算完成。

由索引模型根据 Issue 内容生成。