Create TOC for syntax reference

Refraining from applying this to the introduction for now, although I think we'll want to.

This overall approach is a bit clunky - yet another checked-in piece of autogenerated stuff. I'm making "TOC is out of date" a warning.

CC @nickm, although I'm going to merge this as-is.

assigned to @Diziet

enabled an automatic merge when the pipeline for ba26ea0f succeeds

merged

mentioned in commit ff426255