The browser-based PDF export doesn't pass accessibility checks

The generated PDFs seem to be more accessible after XWIKI-23728, but there are still a few issues remaining, as per https://pave-pdf.org/pave :

• I enabled PDF tagging, but it looks like some tags are incorrectly nested. I hope this will be fixed in future versions of Chrome.
  • e.g. Structure element is incorrectly nested: NonStruct in H1
• Some content is not tagged (so there is still some work left to do on Chrome's side)
  • Missing link alternate description
• It looks like the (mandatory) document title is still not set

I don't see any complains about images, so this XWIKI-19144 might be fixed.