MathJax equation previews

### Have you checked that your feature request isn't already filed?

- [X] I read through [FAQ](https://github.com/alshedivat/al-folio/blob/master/FAQ.md) and searched through the [past issues](https://github.com/alshedivat/al-folio/issues), none of which addressed my feature request.
- [X] Yes, I have checked that this feature request isn't already filed.

### Description & Motivation

I saw elsewhere that it's possible to configure so that hovering over an equation reference can display a preview of the actual equation (much like hovering over footnotes or references shows the linked object in place).

Discussion:
https://gist.github.com/mauriciopoppe/ec311235997fab7b2993

Would it be possible to support this feature?

### Pitch

This is a non-critical but nice-to-have feature that could make reading technical blog posts easier without having to jump back and forth for references.

### Alternatives

_No response_

### Additional context

_No response_