bug#65710: xwidget-webkit cannot play video on Linux

[r09944008]

As title. I visited a website using M-x xwidget-webkit-browse-url and
tried to play the video in it (ex: the video on https://www.gnu.org/),
but webkit hanging infinitely. I think this is a known issue as Po Lu
already flie a ticket to the webkit developers [1]. But currently the
issue is blocked by unable to reproduce the problem in the webkit
side. Hence I opened this one in the Emacs side for tracking and also
wish to raise the attention of Emacs graphics experts to help solving
the problems. Thanks.

[1] https://bugs.webkit.org/show_bug.cgi?id=232860