Add LaTeX package flagderiv to Mathjax

[nofe1248]

Is your feature request related to a problem? Please describe.
I'm a CS student studying type theory, while the Mathjax supports the bussproofs package, it currently lacks support for the so-called "flag-pole" style proof which is quite common in theoretical computer science.

Describe the solution you'd like
I would request Mathjax to add support for the flagderiv package (https://www.ctan.org/pkg/flagderiv?lang=en).

[dpvc]

Thank you for your request. I have marked it as a feature request to be considered in the future, but it is unlikely that it will be addressed any time soon.