[webcomponents] Change createElement(localName, typeExtension) to createElement(localName, { is }) (#408)

In #405 @annevk suggested changing the proposed signature of createElement from (localName, typeExtension) to (localName, options) so that we don't keep piling parameters onto it. This makes sense to me. I think a dictionary containing "is" is pretty reasonable.

This would impact Blink negatively since they are already shipping the string-taking version. I guess maybe they could use an overload for the transition period? Dictionaries and strings are distinguishable, right? I should really memorize that table.

This is all operating under the assumption that we don't just completely remove type extensions from v1. My understanding of the F2F was that we were going to leave them in and see if they got 2 shipping implementations.

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Reply to this email directly or view it on GitHub:
https://github.com/w3c/webcomponents/issues/408