Duplicate margin citations in PDF

Bug description

When I use citation-location: margin and cite the same paper two times in the text, then

• for HTML it will only appear once in the margin, and both occurrences in the text are linked to the item in the margin. This is quite nice!
• for PDF two separate items are created in the margin.

I think it would be nice (and more consistent) if the PDF would also always link the first item, rather than creating a new one. (Or alternatively, if the user had control over what they prefer.)

HTML:

PDF:

Steps to reproduce

See https://github.com/davidpomerenke/quarto-bugs/tree/main/citations.

Expected behavior

Only one citation item in the margin, which is linked by all citation occurrences in the text.

Actual behavior

A citation item for every single citation occurrence in the text.

Your environment

• IDE: latest VSCode
• OS: MacOS Ventura 13.4.1 (c)

Quarto check output

> quarto check
[✓] Checking versions of quarto binary dependencies...
      Pandoc version 3.1.1: OK
      Dart Sass version 1.55.0: OK
[✓] Checking versions of quarto dependencies......OK
[✓] Checking Quarto installation......OK
      Version: 1.3.433
      Path: /Applications/quarto/bin

[✓] Checking basic markdown render....OK

[✓] Checking Python 3 installation....OK
      Version: 3.10.10 (Conda)
      Path: /opt/homebrew/Caskroom/miniconda/base/bin/python3
      Jupyter: 5.2.0
      Kernels: ir, python3

[✓] Checking Jupyter engine render....OK

[✓] Checking R installation...........OK
      Version: 4.2.1
      Path: /Library/Frameworks/R.framework/Resources
      LibPaths:
        - /Library/Frameworks/R.framework/Versions/4.2-arm64/Resources/library
      knitr: 1.39
      rmarkdown: 2.14

[✓] Checking Knitr engine render......OK

Start by rendering the citation example at https://github.com/davidpomerenke/quarto-bugs/tree/main/citations with citation-location: margin for HTML and PDF, then compare how repeated citations are handled. Trace the PDF citation rendering entry point and add coverage for repeated citations; done means one margin item is created and all text occurrences link to it.