Currently, when Wikibase renderes EntityIdValues as HTML, we use the target entity's label as the link's surface text, and the target page's title as the tooltip which is shown on hover (using the HTML title attribute).

Showing the target page title is not very helpful. Instead, we should show the entity ID and the disambiguation description. This would allow users to easily see that a link to Q821229 refers to Berlin, ND, not Berlin, German.

This could be resolved easily be making EntityIdHtmlLinkFormatter put the description (and ID) into the link's title attribute.