Fix ImageCapture API (#2347)

[dodomorandi]

I literally copy-pasted the webidl from the working draft then run the wasm-bindgen-webidl to re-generate the bindings.

It looks fine, even if it could be considered breaking change because the methods depend on different set of features.

Closes #2347

[alexcrichton]

Thanks! To confirm, were all these APIs basically broken and not working before? (asking because there's a bit of breakage)

[dodomorandi]

I think that the API in the webidl file is very old (before December 2016), because I tried going back to a bunch of versions, without encountering something like the onerror attribute. Still being a working draft, there is a good possibility that this API was not used in production, even because the MDN shows a totally different interface respect to the webidl. I did not explicitly try all the APIs, but MDN shows a compatibility table that matches the new API.

In any case, I just realized that the issue #2202 was a subset of this problem.

[alexcrichton]

If this WebIDL is still a draft, perhaps we should move it to the unstable directory?

[dodomorandi]

You are probably right about this: the specs is in working draft, and it's not been touched since 21 June 2017. Surely I would rather have the current spec in the unstable than the old one in enabled. 😊

If you want, I can move the file in this PR, it is a breaking change (even if probably irrelevant) in any case.

[alexcrichton]

The current WebIDL is so old it doesn't work right? If so it seems fine to delete since it doesn't work anywhere anyway.

[alexcrichton]

Thanks!