Add automatic Unity debugging port detection

[walcht]

Having to manually enter the port is just too painful (and relies on luck - since there is no documentation on where Unity listen's to debugging commands on...)

[Namey5]

I've been looking into this while working on Zed integration with unity-dap and it looks like things haven't changed much since the old MonoDevelop implementation.

Unity editor/players will broadcast their presence via UDP multicast on 225.0.0.222:[54997, 4597], with the message including the actual debugging port:
https://github.com/Unity-Technologies/MonoDevelop.Debugger.Soft.Unity/blob/refactor-for-vs-code/PlayerConnection.cs

Failing that, the default debug port Unity uses is derived from the process id:
https://github.com/Unity-Technologies/MonoDevelop.Debugger.Soft.Unity/blob/refactor-for-vs-code/UnityProcessDiscovery.cs#L74

For simplicity I'm currently just using the latter and it seems to work well enough, especially as Zed's debugger provides the process id when attaching to a given process.

[walcht]

@Namey5 - pretty much yes - there are a couple of details with Unity Players but I won't bother.

For the moment, I have a very detailed section on all the methods that can be used to get PORT:IP of both Unity Editor and Player instances:

https://github.com/walcht/neovim-unity#Unity-Debugger-Support

Either way, I will be implementing this since I want a more robust way to constantly get the port:ip pairs.