Showing media feature values

[wbamberg]

@NiedziolkaMichal filed a new PR yesterday: mdn/yari#6566. I haven't tried it out yet but AFAICT it adds a box to media feature pages, showing the current value of the feature on the user's device. It's implemented as a KS macro with some Yari magic behind it.

Without getting into the implementation, I'd like to know whether people think this is a feature we want to have in our pages. At a glance it seems like a nice thing to have, but I might have missed something.

[teoli2003]

I find this very useful. It doesn't add too much cruft to the page and gives something to play with it interactively.