qt: create another indirection X11 window

qt: create another indirection X11 window

The main window may be destroyed before the video window. This notably
occurs if the user requests to close the main UI via window decorations.
While Qt allows those requests to be rejected, doing so would
reintroduce obnoxious bug #4606.

The Qt-X11 display connection will be closed as well as it belongs to
the QApplication instance.

This creates a separate window belonging to a separate display
connection, and which is not tied to the QApplication and QMainWindow
instances. Unfortunately, this adds yet another connection to the X11
display server in the VLC process in addition to QApplication's and the
video display's. And that connection won't process events.

Refs #21875.

Gbp-Pq: Name 0005-qt-create-another-indirection-X11-window.patch