After recent update, `\boldsymbol \partial` renders badly in MathJax 3 (tex-chtml)

Created by: MichaelAllenWarner

Issue Summary

A few weeks ago, \boldsymbol \partial was giving beautiful browser-consistent results in MathJax 3 (tex-chtml), and it looked to be simply the boldface version of the \partial symbol, exactly as expected.

Today, I noticed that it's now giving poor and browser-inconsistent results, and looking at the source code I see that the character is rendered not as the content of a ::before pseudo-element (as is the case with other characters in the equations), but rather as a literal 𝛛 character in a Text node.

Steps to Reproduce:

1. Use the https://cdn.jsdelivr.net/npm/mathjax@3/es5/tex-chtml.js component.
2. Use \boldsymbol \partial in an equation.

Technical details:

• MathJax Version: mathjax@3/es5/tex-chtml.js

Supporting information:

• Live link: https://michaelallenwarner.github.io/physics/2019/07/16/vector-triple-products-in-minkowski-spacetime.html#the-double-curl

• Screenshots of inconsistent browser results (Chrome vs. Firefox):

• MathJax config: https://github.com/MichaelAllenWarner/MichaelAllenWarner.github.io/blob/master/assets/mathjax-prescript.js

• Script tag: https://github.com/MichaelAllenWarner/MichaelAllenWarner.github.io/blob/master/_includes/head.html#L44