XHTTP client: Refactor "packet-up" mode, chasing "stream-up" (#4150)

* Add wroteRequest (waiting for new quic-go)

* Use XTLS/quic-go instead

* Client doesn't need `scMaxConcurrentPosts` anymore

* GotConn is available in H3

* `scMaxConcurrentPosts` -> `scMaxBufferedPosts` (server only, 30 by default)

Fixes https://github.com/XTLS/Xray-core/issues/4100

transport/internet/splithttp/hub.go

@@ -78,7 +78,7 @@ func (h *requestHandler) upsertSession(sessionId string) *httpSession {
 	}
 
 	s := &httpSession{
-		uploadQueue:      NewUploadQueue(int(h.ln.config.GetNormalizedScMaxConcurrentPosts().To)),
+		uploadQueue:      NewUploadQueue(h.ln.config.GetNormalizedScMaxBufferedPosts()),
 		isFullyConnected: done.New(),
 	}