Add ability to change shell executor for language servers/internal processes

[Tefached95]

Trying to set up erlang-ls on Windows, I compiled it and generated the required binary, which I placed in my PATH. Running it in bash works properly. However, trying to execute the binary from the command prompt or PowerShell results in a "not a proper executable" error.

Curiously, the which rust crate will not find an extensionless executable in the PATH despite the fact that running which erlang-ls properly finds the file.

This can be "fixed" by adding an .exe extension manually but when opening an erlang file, the language server fails to start, and the log shows the following line:

2022-12-09T15:44:13.904 helix_view::editor [ERROR] Failed to initialize the LSP for `source.erlang` { IO Error: This version of %1 is not compatible with the version of Windows you're running. Check your computer's system information and then contact the software publisher. (os error 216) }

My proposal is to make the shell executor configurable for internal processes, such as running the language servers, something akin to the editor.shell property. Maybe I'm going about this the wrong way but so far I haven't been able to find a workaround for running erlang-ls on Windows in helix.

[archseer]

There is no shell used, the server is started directly as a subprocess.

[Tefached95]

Should we then consider this a bug? At least in my eyes this is a valid use case and it's not working as expected.

[the-mikedavis]

Is Helix built for Windows on your machine? I'm not very familiar with Windows or WSL but we may not be able to call a WSL program from a Windows program in the same way that command prompt / PowerShell can't execute erlang-ls.

FWIW the code to execute the language server as a child process is here:

helix/helix-lsp/src/client.rs

Lines 59 to 67 in bdeefbf

	let process = Command::new(cmd)
	.envs(server_environment)
	.args(args)
	.stdin(Stdio::piped())
	.stdout(Stdio::piped())
	.stderr(Stdio::piped())
	// make sure the process is reaped on drop
	.kill_on_drop(true)
	.spawn();