feat: add alt text to generated latex images

[domoritz]

See latex3/latex2e#651.

If you add \DocumentMetadata{testphase=phase-III} to the beginning of the document, this might just work. See https://www.latex-project.org/publications/2023-UFi-FMi-TUG-tb137fischer-tagging23.pdf for details about the state of tagged documents.

[jheer]

Cool! Would be great to check if this works. Also we'd want to make sure we don't get errors or any others issues when running through a pdflatex version that doesn't support alt text.

[domoritz]

I've been using the alt texts for a while now without problems but have not had success with latex experimental mode to embed alt texts and render complex templates correctly. This change is more forward looking for when latex fully supports this but I think having documents ready now is good since it will make any document that gets recompiled in the future automatically more accessible (e.g. if someone posts a paper on arxiv).

[domoritz]

So in short, this doesn't cause any harm but also has no benefit right now. I think it's still good to merge so that current papers become accessible in the (hopefully near) future.