Configure mathjax in sphinx config, and not in a javascript file. In this way, we can get ride of the custom theme option mathjax_macros, which is not understood by other themes. This is preparation to support the furo theme, see #33601.

We also upgrade Mathjax to v3. The configs were migrated using
https://mathjax.github.io/MathJax-demos-web/convert-configuration/convert-configuration.html
with the following manual changes:

• Remove processEscapes since this now defaults to true in v3 anyway.
• Remove ignoreHtmlClass/processHtmlClass since they are set to the default values.
• Remove noerrors extension, which hides error messages. Normally, there shouldn't be any errors and, if there are, its probably good to have them displayed very prominently so that reviewers can discover these issues. But I don't feel very strongly about this change. Reference: https://docs.mathjax.org/en/latest/input/tex/extensions/noerrors.html

Refs #25833

Depends on #25833

CC: @kwankyu @strogdon @haraldschilly @mkoeppe

Component: documentation

Branch/Commit: public/docs/mathjax_ext @ 89ec417

Reviewer: Kwankyu Lee

Issue created by migration from https://trac.sagemath.org/ticket/33600