Use BCD to automatically disable experimental APIs

[saschanaz]

From #816 (comment).

It's burdensome to manually check whether there are stable implementations for every spec update. Fetching data from BCD will help reducing such burden and may also enable autoupdating.

(Assigning this to myself)

[HolgerJeromin]

Just a reminder for those with a bad memory (like me): BCD is https://github.com/mdn/browser-compat-data here :)

[saschanaz]

#1034