This method allows a listening port to process connections with
different protocols.  It lets the websocket server handle a TCP
socket, upgrading it to a websocket

[ChangeLog][QWebSocketServer] Add support to handle external QTcpSocket

Done-with: André Klitzing <aklitzing@gmail.com>
Task-number: QTBUG-54276
Change-Id: Ia36b481dc87d6f3806e9f1e61e75e528640f1937
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>