WebIDL `async iterable` is now `async_iterable`

[schenney-chromium]

I was sent here by https://github.com/whatwg/webidl to report a syntax change in WebIDL.

Issue web-platform-tests/wpt#54029 renamed async iterable to async_iterable and specs have been updated. Browsers will start to accept this moving forward.

[HolgerJeromin]

As far as I understand this is already done:

#2087

[schenney-chromium]

Yes, that's it by the author of the WebIDL spec change.