Adding Abort to C# Websocket

[rekhoff]

Description of Changes

The implementation of a solution to #3044 , this adds an Abort function to the WebSocket, which runs if Disconnect is called when the WebSocket is not connected.

API and ABI breaking changes

Not API breaking.

Expected complexity level and risk

1

Testing

• Test locally with a C# CLI test client.
  Note: Before change (either on Rust of C# server), server would see 4 Debug log entries about connecting, but not see the Info log about the client connection ending like would normally be seen in a disconnect. After change, server shows no log entries at all, because connection is properly aborted.
• Test locally with a C# WebGL test client.

[jdetter]

since the contents of the if statements are the same, maybe let's just #if/#else the if statements themselves?

[jdetter]

e.g.

            if (webSocket.IsConnected)
            {
                webSocket.Close();
            }
#if UNITY_WEBGL && !UNITY_EDITOR
            else if (webSocket.IsConnecting)
#else
            else if (webSocket.IsConnecting || webSocket.IsNoneState)
#endif
            {
                webSocket.Abort(); // forceful during connecting
            }