MathJax 4.0 support

[randolf-scholz]

MathJax 4.0 was released in August (https://github.com/mathjax/MathJax/releases/tag/4.0.0), it has tons of new features, so support in sphinx would be awesome.

[randolf-scholz]

In particular, Pre- and Post-filters look very interesting: https://docs.mathjax.org/en/v4.0/advanced/synchronize/filters.html

[randolf-scholz]

One could probably consider deprecating MathJax 2.0 as well, the last release was in 2020.

[mgeier]

I have created #14080, would be great if you could test it.

In the meantime, you can manually switch to MathJax v4 with this in your conf.py:

mathjax_path = 'https://cdn.jsdelivr.net/npm/mathjax@4/tex-mml-chtml.js'

You can use mathjax3_config for MathJax 4 as well.

If you find any incompatibilities, please let me know!