[FR] Add a Typst document format

[cderv]

Pandoc now support producing Typst document to produce nice PDF. It could be interesting to bring support to this through a typst_document() format, or a pdf_document variant - like a new pdf_enfine: typst argument, or pdf_typst_document() format.

This could require some work in knitr too to improve code output support for typst feature, if Pandoc has limitation.

Related also to

• [FR] Typst Support bookdown#1439