C++ Doxygen documentation & many doc improvements

[Wumpf]

What

Try it yourself:
https://wumpf.github.io/rerun-cpp-doc-test/
(yes I sacrificed a repo for this ;))
Or to get a perfect up to date version now and in the future just run pixi run cpp-docs, the docs appear then in rerun_cpp/docs/html/index.html

• fixes almost C++ API Docs webpage #3974
• Missing are:
  • process to upload it to landing and link it up in our docs
  • more thorough pass to improve docs overall
    • lots of stuff is undocumented. We should consider making this an error in doxygen (I disabled it for the time being!)

After some back and forth I landed with a pure doxygen documentation using the impressively good https://jothepro.github.io/doxygen-awesome-css/ css.
To avoid submoduling and make customization easy, the theme is embedded in our repo.

Otherwise tons of improvements on our doc strings. Started a guide on how to write docs similar to what we have for python.

Quite happy with it as-is already. Some of the doc improvements to be done are also related to smaller code refactors I want to do :)

Review tip: The first commit contains the default doxygen file, if you want to know what I changed about it just exclude it.

Bunch of screenshots for the lazy:

Checklist

• I have read and agree to Contributor Guide and the Code of Conduct
• I've included a screenshot or gif (if applicable)
• I have tested demo.rerun.io (if applicable)
• The PR title and labels are set such as to maximize their usefulness for the next release's CHANGELOG

• PR Build Summary
• Docs preview
• Examples preview
• Recent benchmark results
• Wasm size tracking

[teh-cmc]

Straightforward and works great.

Problem for later: namespaces section looks empty:

[Wumpf]

Problem for later: namespaces section looks empty

Hmm good catch. I'll look into this after landing!
Somehow that's not the case on https://docs.opencv.org/5.x/namespaces.html (which uses the same theme)