Consider moving active development to the repo with more stars

[jaltekruse]

Issue Summary

The move to use a completely new repository for the more recent versions of MathJax has created some confusion a the the project's current level of active maintenance. A few years ago I chimed in a Hacker News thread to defend that the project was not abandoned, which was claimed in an article talking about the release of math embedding in Github markdown.

https://nschloe.github.io/2022/05/20/math-on-github.html

https://news.ycombinator.com/item?id=31450597#31457631

Today I ran into an issue with MathJax and went to go looking to see if there were discussions already about the behavior I was seeing (there are), but I then realized that this bug tracker is being used as the primary one still.

There are a number of projects on GitHub that were previously quite active, still have lots of users reporting issues, but have slowed down development significantly. Right now to a certain extent MathJax presents that way. This also hurts MathJax for rankings on sites like this OssRank thing, which currently has entries tracking Katex and Math.js, but no entry for MathJax.

https://ossrank.com/p/3772-math-js

I believe these aggregator things often scrape from similar APIs to the "contributors" page on github, which generally only reports activity on the "main" branch or whatever you designate as the primary branch.

I am assuming that the choices for the separate repo and using a "develop" branch are intentional, but I did want to highlight that there are some advantages to following a more traditional project structure.

Some possible suggestions:

1. Add a link to the currently maintained repo from this repo's README, as this repo comes up first in search
2. Possibly mark the "develop" branch as the primary on that other repo, so it is more obvious that very active development is still happening.
3. Maybe move active development under this repo, moving the current tree to a branch called something like "legacy" and making this the home of all current MathJax happenings. It will allow you to build from the larger number of stars this repo has, and will help the project in various rankings. You could still keep that repo around for the separate issue tracker for project maintenance things, but maybe just as a separate issue tracker.

Steps to Reproduce:

Not really relevant

Technical details:

Not really relevant

Supporting information:

[jaltekruse]

I created a PR for adding a link to the new repo in the README - #3383