[Tooltip] Perfomance issues

I know this might require quite a refactor, but tooltip performance should be improved. It's particularly bad when you have several (let's say dozens) of tooltips on a page, because for every tooltip a new element is added to the DOM (and the initialisation process sometimes takes a bit).

Several popular JS tooltip plugins use a different approach in which a single element is created and the content on this element is updated when triggering the different tooltips. Couldn't a similar approach be implemented?

Start by locating the tooltip implementation and examining how tooltip elements are created and initialized when a page contains many tooltips. Reproduce the slowdown with dozens of tooltips, then compare performance after the implementation uses a shared element and updates its content as described; done means the multi-tooltip case is measurably improved without changing tooltip behavior.

Written by the indexing model from the issue text.