bug#62407: 30.0.50; The command to run elixir-ls on Windows is `language_server.bat`

[Eli Zaretskii]

> From: 牟 桐 <mou.tong@outlook.com>
> CC: "62407@debbugs.gnu.org" <62407@debbugs.gnu.org>
> Date: Fri, 24 Mar 2023 02:22:44 +0000
> 
> 
> > What is the value of shell-file-name on that Windows
> > system?
> 
> It's `cmdproxy.exe` on Windows, after I changed it to `powershell.exe`
> and `cmd.exe`, the eglot's guess stays the same. I guess that is because
> eglot had hardcoded the result here:
> 
> https://github.com/emacs-mirror/emacs/blob/4566a0c6b825a18e6c065da0543b8b942b7db8df/lisp/progmodes/eglot.el#L224-L225
> 
> ``` emacs-lisp-mode
> ((elixir-mode elixir-ts-mode heex-ts-mode)
>  . ("language_server.sh"))
> ```

I'm not saying that the current code is correct, I'm just saying that
the condition to use language_server.bat should be based on the value
of shell-file-name, not on system-type, because some people use Bash
on Windows as well.

Btw, is language_server.bat part of that server's distribution, or did
you write the batch file yourself?