[3.x] Add --lsp-port as a command line argument

[ryanabx]

This PR is a cherry-pick of #81844 , which was accepted this week.

Implements an --lsp-port command line argument for Godot. This argument overrides the user's editor setting for network/language_server/remote_port.

The use case for this argument would be for the godot-vscode-plugin to be able to specify the port used for the language server instance spun up by the plugin.

This would potentially solve a few long standing issues with the godot-vscode-plugin, including:

Godot's 3.x LSP port and 4.x LSP port don't match, causing the plugin to have to tell users to explicitly specify the port they have selected in their editor settings. (See godotengine/godot-vscode-plugin#473)
Spinning up multiple workspaces in vscode would cause both to use the same language server.
If the change is accepted, it should be cherry picked to 3.x. I can help with that if need be.

Let me know what things I have to change. Since this is my first time working with main.cpp and further with #ifdef and #ifndef, please pay attention to my use of those and let me know if they are up to standard.

I also added the port to the language server editor print that says --- GDScript language server started ---, changing it to --- GDScript language server started on port "port"---.

Bringing this change to 3.x will allow the godot-vscode-plugin's upcoming support for the argument to work in 3.x as well. Otherwise, the command line argument will just pass through.

[akien-mga]

Thanks!