Add special span classes

[cwickham]

Closes quarto-dev/quarto-cli#12073

Adds an "Other Spans" section: Preview

[github-actions]

🚀 Deployed on https://deploy-preview-1601.quarto.org

[cwickham]

@cderv I checked these on the "big" formats: html, pdf, typst, docx, revealjs, and pptx.

example.qmd

---
title: "Special Spans"
format: 
  html: default
  pdf: default
  docx: default
  typst: 
    output-file: special-spans-typst.pdf
  revealjs: 
    output-file: special-spans-reveal.html
  pptx: default
---
Quarto
[This text is smallcaps]{.smallcaps}
[This text is underlined]{.underline}
[This text is highlighted]{.mark}

They all work with the exception of:

• .mark with format: typst. I've opened a pandoc issue.
• .mark with format: pptx. 🤷🏻‍♀️

Is it worth calling out the exceptions?

[cderv]

The .mark feature is from Pandoc itself: https://pandoc.org/MANUAL.html#highlighting

They do not help much by saying 😅

This will work in all output formats that support highlighting.

So Typst should support it in next version : jgm/pandoc@82668ff

And it is possible that PPTX does not support it. So we could mention it.

[github-actions]

🚀 Deployed on https://deploy-preview-1601.quarto.org

[github-actions]

Successfully created backport PR for prerelease:

• [Sync to prerelease] Add special span classes #1609