www/qt5-webengine: Enable support for WebRTC and video capture devices

When accessing video capture devices warnings like below are emitted [2]:

[40533:463527936:0420/214650.072475:ERROR:create_video_capture_device_factory.cc(58)] Not implemented reached in std::unique_ptr<VideoCaptureDeviceFactory> media::(anonymous namespace)::CreatePlatformSpecificVideoCaptureDeviceFactory(scoped_refptr<base::SingleThreadTaskRunner>)

Also websites that want to access the camera, microphone, etc. exhibit
broken behavior, e.g. no dialogs to permit access on the desired capture
devices come up. [1]

Thus add the related patches from www/chromium [2] that enable support for
video capture devices and explicitly activate the WebRTC feature. [1]

PR: 236915 [1], 237423 [2]
Submitted by: cmt [2]
Reported by: thea20lineisameme@protonmail.com [1]
Reviewed by: rakuco, tcberner (kde), Lorenzo Salvadore
Approved by: tcberner (kde)
Differential Revision: https://reviews.freebsd.org/D19900