feat: Upgrades to MathJax version 3 and supports setting different configuration files (defaults to 'tex-mml-chtml').

[HouJP]

Introduction

This PR is used to upgrade to MathJax version 3 and supports setting different configuration files (defaults to 'tex-mml-chtml).

It is inspired by the issue: mdBook doesn't support mathcal symbols.

Closes #2284.

Background

This PR can fix a bug hidden in MathJax v2 introduced here.

[ehuss]

Thanks for the PR! I believe #1918 is already open to address this. Can you give it a try and see how it works for you?

[HouJP]

Thanks @ehuss!

I took a quick look and I think it will also solve the problem.

The advantage of that PR is that it's more flexible (e.g., local js), but its disadvantages are

1. It requires larger changes to the configuration compared to this PR.
2. It's NOT compatible with existing configs.

The advantages of this PR are

1. This is a tiny change.
2. It is compatible with previous configs.

I respect the owners' / reviewers' decision. Please feel free to let me know if you prefer to withdraw this PR.

[expikr]

I prefer this PR because it makes #2069 much easier

[edwardzcn-decade]

Can @ehuss review this PR again? I meet the same problem in #2284 and I think it is common when using mdbook in macOS 13 Ventura and above (for me it is macOS 15) because Apple shipped the fonts which used by mathjax render v2 and left some mismatches since macOS 13.

Now your mathjax test markdown does not display italics properly on most Apple computers, and differs greatly from the schematic #2070. Also using mathcalsymbols causes formulas to not show up at all (Mathematical Calligraphic Font mismatch).

This PR just upgrade to MathJax v3 with almost the same configuration