Reimplement LaTeX setup snippets using lthooks

[Witiko]

Since version 2.10.0, the Markdown package has allowed users to define and invoke snippets that have a local effect on the behavior of markdown elements. By reimplementing snippets using @FrankMittelbach's lthooks instead of general TeX commands, it will be easier for different packages to modify one snippet without stepping on each other's toes.