[Idea] Move Receive() to it's own Listen() method

首先阅读 Websocket.cs 及其 WebGL 实现。将 Receive() 调用与 Connect() 分离，添加 issue 中描述的 Listen() 方法和 WebGL 兼容方法，然后验证调用方可以 await Connect()，并从 open handler 开始监听，而无需进行特殊的 WebGL 处理。

Current Receive() is called at the end of Connect(). This means that if you ever want to await the Connect() call (so that you move on when it's connected), it won't actually return until the socket is disconnected. Moving it to it's own Listen() method would allow for that.

Something like:

// Websocket.cs
// 1) Remove the "await Receive()" call from the end of Connect()
// 2) Add an empty Listen() method in the WebGL implementation for compatibility
// 3) Add the following method:
public async void Listen()
{
	try
	{
		await Receive();
	}
	catch (Exception ex)
	{
		OnError?.Invoke(ex.Message);
		OnClose?.Invoke(WebSocketCloseCode.Abnormal);
	}
	finally
	{
		if (m_Socket != null)
		{
			m_TokenSource.Cancel();
			m_Socket.Dispose();
		}
	}
}

This lets you handle the websocket connection like so:

// WebsocketConnection.cs
public async Task ConnectAsync( string uri )
{
	if( this.isOpen )
	{
		Debug.LogWarning( "[WebSocketConnection] Trying to connect a websocket, but we're already open" );
		return; // we're already connected
	}

	// start our connection
	this.m_uri = uri;
	this.m_socket = new WebSocket( this.m_uri );
	
	// add our events
	this.m_socket.OnOpen += this._onWebSocketOpen;
	this.m_socket.OnClose += this._onWebSocketClose;
	this.m_socket.OnError += this._onWebSocketError;
	this.m_socket.OnMessage += this._onWebSocketMessage;

	Trace.Log( $"[WebSocketConnection] Opening a new connection to {this.m_uri}" );
	await this.m_socket.Connect();

	// wait until the socket is actually open
	await new WaitUntil( () => this.isOpen );
}

public void Update()
{
#if !UNITY_WEBGL || UNITY_EDITOR
	if( this.isOpen )
		this.m_socket.DispatchMessageQueue();
#endif
}

// called when our socket is open and ready for business
private void _onWebSocketOpen()
{
	Debug.Log( $"[WebSocketConnection] Connection to {this.m_uri} open!" );

	// start listening on the socket (NOTE: we're not awaiting here)
	this.m_socket.Listen();
}

Then actually using it in a method becomes much simpler. You can connect with something like:

public async void JoinGame()
{
	// check if we need to connect
	if( !this.m_websocketConnection.isConnected )
		await this.m_websocketConnection.ConnectAsync( this.m_websocketServerURI );

	this.m_websocketConnection.JoinGame();
}

As an added benefit, you don't need special handling for WebGL and nothing blocks unless it should