Make macros work in ZIPs

[daira]

Ideally, macros could be defined in LaTeX \newcommand format in a file that is imported by the protocol spec and ZIPs (also see #227).

Some macros, while semantically the same, might need to be defined slightly differently between the spec and ZIPs due to rendering differences between LaTeX and KaTeX. That's easy to handle because the spec can just import the common file and then use \renewcommand to define its variants. It's also possible to define low-level macros to handle the rendering differences and then define the high-level ones in terms of those.

The macro file used by the VS Code previewer can be generated from the common file, in the same way as in wg-plonkish (from a currently unmerged PR zkpstandard/wg-plonkish#57).