Windows and WSL

[llogick]

See zigtools/zls-vscode#56 and zigtools/zls#1137

Vague idea:
Add a ${arch}-${os} subfolder here const installDir = vscode.Uri.joinPath(context.globalStorageUri, "zls_install");
Treat zls.path as an override - if set user is responsible for managing the executable (could still ask to install if it fails to start or if older then set to null -> use InstallDir)
Starting client: check zls.path == null (and =="") -> use InstallDir