Support for Device Frames

[ethankusters]

@jack

I thought that this file was included in the DocC catalog, so in theory it would be possible to consume the data. If that's not always the case and we can't provide diagnostics and autocomplete for this feature then I am not in support of the way device frames are declared.

I agree and I think that is the reason this feature is being pitched as "experimental":

@dhristov

I’m excited to share a proposal for a new experimental feature that allows authors to wrap images and videos inside device frames.

In order to have to proper (non-experimental) support for device frames Swift-DocC will need to have some story for out-of-the-box support of frames so that the average user doesn't need to declare them at all. I believe this is being left to a future pitch. (In general we also need a better story for the UX of theming – diagnostics, etc – and I think improvements to declaring custom frames will come with that).