[dom] Merge DOMSettableTokenList into DOMTokenList (#119)

Per discussion on IRC with @domenic and @zcorpan only HTML uses these classes. It seems like we could simplify things a bit by merging them into a single class and use `[PutForward]` everywhere.

The problem I could see is that libraries depend on changing the prototype of these classes in ways that are incompatible with such a simplification. What do folks think?

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Reply to this email directly or view it on GitHub:
https://github.com/whatwg/dom/issues/119