Upgrading Mathjax to version 4

[Ethsim2 (Ethan)]

I’m currently on latest-release +17 on a fairly math-heavy production instance.

Really nice to see [grid] now working properly on Meta - that’s a big quality-of-life improvement for math-dense posts. I’m happy to compromise on [center] where needed.

For context, I previously ran into some edge-cases around math inside [grid] / [details], which I documented here (in case it’s still useful):

Inline KaTeX/MathJax $...$ inside [grid] can leak BBCode when used with [details]

i thought i should at least conculde mathematically accurate information, not ChatGPT waffle \frac{1}{r^2 \sin\theta} \left| \begin{matrix} \textcolor{orange}{\hat{r}} & r\hat{\theta} & r\sin\theta\,\hat{\phi} \\ \partial_r & \boxed{\partial_\theta} & \boxed{\partial_\phi} \\ A_r & \boxed{r A_\theta} & \boxed{r\sin\theta\, A_\phi} \end{matrix} \right| \frac{1}{r^2 \sin\theta} \left| \begin{matrix} \textcolor{orange}{\hat{r}} & r\hat{\theta} & r\sin\theta\,\hat{\phi} \\ \p…

Thanks again to everyone working on the MathJax 4 upgrade - it’s great to see this level of polish landing.