Create Annex B lib target

 [Annex B](https://www.ecma-international.org/ecma-262/6.0/#sec-additional-ecmascript-features-for-web-browsers) is the 🚽 of JavaScript with such features like a broken `escape` method and the `blink` method for `string`s. We shouldn't offer broken functions by default, and (almost) no one wants to see `fontcolor` in their string completion list, but it *is* "standard", so we should have a separate `lib` target (in the same category as e.g. `dom`) for `annex-b` that squirrels away the Annex B declarations so people can still opt in if they want to.