Fix \textit, etc., when used with text-macros extension. (#2514)

Davide P. Cervone
2023-03-19T19:07:24Z

This back ports the fix from PR mathjax/MathJax-src#546 that allows `\textit{}` and related macros to work when the `text-macros` extension is used.

Resolves issue #2514.