Simple interface to change the font of the non-math part of LaTeXString

[Kolaru]

Original issue: https://github.com/JuliaPlots/Makie.jl/issues/1560

We should have a simple way to change the font of the the normal text in the LaTeXStrings.

I'm thinking of something like generate_texelements(latex_string, textfont="NewComputerModern").

This is possible as long as font modifiers are not available outside of math mode, since that would require 4 different fonts (roman, italics, bold, and bold italics).