Support using fish as the default shell on Windows msys

[ahaoboy]

This only happens when fish is used as the default shell. If only PowerShell is supported on Windows, is it possible to force PowerShell to be used instead of a user-defined shell?

If I set powershell or cmd as the default shell, there will be no problem, but it is not a very user-friendly experience to switch shells every time you debug.

rust-lang/rust-analyzer#19372

[vadimcn]

CodeLLDB does not interact with the shell directly - it simply tells VSCode to execute a command in the terminal. The rest is up to VSCode. It looks like there’s a limitation in its Fish shell support?