[Feature Request] equation preview with extra math packages

[garylavayou]

Is your feature request related to a problem? Please describe.
The preview environment seems not to support the commands \bm and \mathclap, which are in the package bm and mathtools.
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Describe the solution you'd like
As latextools does, an option could be added to the LaTeX Workshop, so that users can add extra math related packages that are also used in their tex files.
In this way, the preview should be correctly rendered.

Describe alternatives you've considered
Or the requested packages could be included in the built-in preview settings.

[jlelong]

From stackoverflow

You can not simply drop a LaTeX package into MathJax. The packages that MathJax supports have to be re-implemented in javascript, which is difficult for non-trivial packages

Mathtools is not supported by mathjax, see mathjax repo

[xinleiyu]

\bm is recommended by some as the best option for LaTeX, but not supported by MathJax.

Can we change the config as follows to replace \bm with \boldsymbol in preview?

TeX: {
  Macros: {
    bm: ["\\boldsymbol{#1}",1],
  }
}

From the issue of MathJax: LaTeX input: add support for bm package

[tamuratak]

https://github.com/James-Yu/LaTeX-Workshop/wiki/Hover#latex-workshophoverpreviewnewcommandnewcommandFile