aria attributes may be incorrect

[kaleb]

Currently the core-tooltip attribute gets the role="tooltip" attribute applied to it, but I believe this is incorrect. Shouldn't it be the div#tooltip element that needs role="tooltip" and the core-tooltipe element should have aria-describedby="tooltip"?

I understand that that relying on the tooltip id of the div#tooltip element in the shadow dom may not work in any user agents, because most accessibility user agents don't consider non-unique IDs (a la shadow dom). This was just an issue I wanted brought up.