Typst callout without body

[debdagybra]

See #9763

[cscheid]

Thanks for the PR. Before we can merge, we need you to sign and submit a CLA: https://github.com/quarto-dev/quarto-cli/blob/main/CONTRIBUTING.md

I also would like to understand how this works across formats. I believe it works for HTML, but it might have been by accident.

We'd like to at least test:

• html
• revealjs
• pdf
• typst
• docx

[debdagybra]

Before we can merge, we need you to sign and submit a CLA: https://github.com/quarto-dev/quarto-cli/blob/main/CONTRIBUTING.md

Done :)

You were right, the behaviour isn't consistent in all formats

Currently, when the body of the callout is empty:

• html and revealjs don't show the body part
• pdf (tinytex), typst and docx show an empty body part.

[cderv]

Interestingly, same report on revealjs

• Title only callout in revealjs causes error #9821
  So we need I guess to extend this PR for good support on all formats.

[cscheid]

I'm going to merge this one and start a new issue for tracking all different cases in callouts.

[cscheid]

Thanks for the PR, @debdagybra!