Honor `X-Forwarded-Port` header

[mering]

• VS Code Version: latest
• OS Version: Linux

Steps to Reproduce:

1. Run ./scripts/code-server.sh --port 3000

2. Run an nginx proxy with the following config:

   server {
       listen 8080;
       listen [::]:8080;
   
       location / {
           proxy_set_header X-Forwarded-Host $host;
           proxy_set_header X-Forwarded-Port $server_port;
           proxy_set_header Host $host;
           proxy_set_header Upgrade $http_upgrade;
           proxy_set_header Connection $http_connection;
           # Destination
           proxy_pass http://localhost:3000/;
       }
   }

3. When accessing http://localhost:8080/, it cannot connect the WebSocket

When using proxy_set_header X-Forwarded-Host $host:$server_port; instead of the separte host and port headers, everything works fine.

[mering]

I fixed this in ee80e47f084e4cab294fe15fa5ec15b7b5fc9f6c as part of #210455. If you prefer, I can move this to a separate PR.