Docs: Replace sphinx-tabs with sphinx-design

[benjaoming]

We already have sphinx-design in use and it provides a tab widget that can replace sphinx-tabs.

This includes:

• Refactor current use of tabs::
• Update expand-tabs.js, note that it has been expanded to include Sphinx labels through URL anchors in diataxis/main
• Check that reference labels work inside tabs!
• Revert Move reference labels outside of tabs #9866

#9855 deals with a set of warnings possibly caused by sphinx-tabs and potentially solved by using sphinx-design instead, but we haven't investigated that.

[benjaoming]

I was chatting with Executable Book people and as I understand it, sphinx-tabs is well-maintained and will likely continue to exist.

It's a bit like Unix philosophy for Sphinx extensions... "do one thing and do it well"

I actually prefer the look&feel of sphinx-tabs, and since we already have a bit of custom JS logic to auto-open tabs, I think we should actually keep sphinx-tabs around and expect it to be there for the longer run :)

[benjaoming]

Btw... sphinx-tabs supports Sphinx 6 already... and sphinx-design doesn't yet.