Truncate extension descriptions

This is for #8216.

- [x] Code to toggle between original and truncated description
- [x] Visual review
- [ ] Code review
The old comment is gone. So i'll reply here.

You are not really using the classes to style the element, so maybe you shouldn't use a class. To store data in the DOM use the data attributes. You can just have a single `data-*` attribute and change i'ts value.