[meta] Improve the accessibility of the Token module

Thanks for starting this, well aware that accessibility and usability of the token UI is really not great. (And performance!).

Frontend stuff is really not my area of expertise, so I can't help much there, but I can try to review and commit things that are reviewed and approved by others.

That said, I'm not sure if granular improvements are feasible or the whole thing should be redesigned from scratch, which is what 📌 Token UI 2.0 Active would be about.

If you have any knowledge of existing tools that could be used for such a purpose, that are better at those things out of the box than the old jquery treetable then that would be great. One of the main things it would need to support is partial/lazy loading of the structure so we avoid to load hundreds of tokens upfront and get rid of the depth limit at the same time.

Very open to alternative UI approaches as well, I've been thinking about about some kind of mix of autocomplete and tree traversing.

What a great side effect of the Drupal CMS initiative, lifting up collectively the rest of Drupal as well, making an already amazing module even better. Nice!