[feature suggestion] Add a V4L source module

[yurivict]

So that Radiance would be able to read from the webcam.

[ervanalb]

You can actually do this already using the MPV block. Just type in /dev/video0 into the prompt and you should get your webcam. There is also a super hacky way to pass arguments like resolution, but I forget how it works (not at a computer right now, sorry)

[zbanks]

@yurivict does the MPV block work for you? It's under "Custom" in the library. MPV supports a pretty wide variety of URLs and parameters, you can see resources/qml/Instantiators/YoutubeInstantiator.qml as an example of an MPV-based node that builds an MPV-accepted URL from a youtube search query.