[webidl] iterable interface iterators should return the actual key (or the value if there is no key) not an index (#67)

See <https://bugzilla.mozilla.org/show_bug.cgi?id=1085293#c10>.  Basically, two-type iterables should act alike Map and one-type ones should act like Set, instead of acting like Array.

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Reply to this email directly or view it on GitHub:
https://github.com/heycam/webidl/issues/67