qt/x11: also pass the window for gstgl -> qt context
qt/x11: also pass the window for gstgl -> qt context

Removes this warning from Qt:

QGLXContext: Multiple configs for FBConfig ID -1
QSGContext::initialize: depth buffer support missing, expect rendering errors

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-good/-/merge_requests/575>

pexip/gst-plugins-good,pexip/gst-plugins-good,GStreamer/gst-plugins-good,GStreamer/gst-plugins-good,pexip/gst-plugins-good,pexip/gst-plugins-good,GStreamer/gst-plugins-good,GStreamer/gst-plugins-good,pexip/gst-plugins-good