Unable to debug external processes

I confirmed the problem with the debugger for Unity. (`unity.unity-debug`) The extension had two problems on Flatpak:
1. Mono is not available via `PATH`.
2. Cannot enumerate external processes.

1 can be easily solved by adding yet another SDK to `code.sh`. The question is how to resolve 2. I suspect any other debugger attaching to existing processes has the same issue and adding the permission for that operation will be beneficial for them, but that can also effectively disable the sandbox.

先阅读 code.sh，以了解 Mono SDK 如何通过 PATH 暴露，然后检查与枚举外部进程相关的 Flatpak 权限。确认对 unity.unity-debug 附加调试器是否有效，以及是否可以在不禁用 sandbox 的情况下添加所需权限。

由索引模型根据 Issue 内容生成。