Add experimental ViewTransition interface

[tigerros]

This adds the experimental ViewTransition interface. See MDN docs and W3C specs. I hope experimental APIs are allowed.

I followed the contributing guidelines, but let me know if I did something wrong.

[daxpedda]

LGTM!
Could you add an entry to the changelog?

[tigerros]

Added.

[daxpedda]

Thanks!
Just waiting for CI.

[tigerros]

@daxpedda I wanted to ask an additional question, when can it be moved into the webidls/enabled directory? I looked at the contributing guide and there was no mention of this.

[daxpedda]

We don't have any official guidelines for this. Basically when we think that the API isn't going to change anymore.

It's a candidate recommendation, so I'm assuming this isn't going to change anymore, but it's only implemented by Chromium and has very low usage across the web.

Considering how close this is to recommendation I would prefer to wait unless there is a strong incentive otherwise.

[tigerros]

Alright. If you're wondering, the reason why I added this is because someone requested this as a feature (as in, a framework API around it) in Dioxus, which is an SPA framework and thus would benefit quite a bit from this.