Support figure divs in LaTeX

[multimeric]

Currently if you e.g. render https://github.com/multimeric/Fwrappe/blob/main/examples/figure_div.qmd to PDF, it will fail to wrap. This is because the figure classes get thrown out and only the image classes remain by the post-render phase that the filter runs.

Some possible solutions:

• Configure when the filter runs, but this is blocked by Filter extensions can't be specified in combination with processing phases quarto-dev/quarto-cli#11750.
• Allow the user to attach the class to the Image element, and then copy this to the parent figure. This would be a hack but user friendly enough.
• Add a second extension that runs before quarto. Unfortunately due to YAML Validation fails for specifying filter process positions in extensions outside of formats quarto-dev/quarto-cli#11560 (comment), this would have to live in another repo and the user would have to add both.