gh-101100: Add a table of class attributes to the "Custom classes" section of the data model docs

[AlexWaygood]

• Convert the attribute references in the "Custom classes" section to a list table
• Refer to the attributes as type.__*__ rather than class.__*__; this reflects the reality at runtime
• Make sure all attribute references for custom classes are referenceable from other files
• Add references for attributes that were not previously documented (such as __qualname__), and move some references from library/stdtypes.rst to the datamodel docs so that references for all class attributes can be found in a single location
• Update and improve references to class attributes from other files so that they properly link to the canonical entries in the table
• Fix 21 or so Sphinx nitpicks in the process

• Issue: Fix all Sphinx reference warnings in the documentation #101100

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📚 Documentation preview 📚: https://cpython-previews--124480.org.readthedocs.build/

[willingc]

Looks good @AlexWaygood. Thanks for doing this table.

As an FYI, it's much faster to review when the nitpick fixes are a separate PR. Makes it a little easier to grok what the new addition contains. No worries for this PR.

[AlexWaygood]

As an FYI, it's much faster to review when the nitpick fixes are a separate PR. Makes it a little easier to grok what the new addition contains. No worries for this PR.

Thanks -- I'll separate it out into two PRs next time!

[miss-islington-app]

Thanks @AlexWaygood for the PR 🌮🎉.. I'm working now to backport this PR to: 3.12, 3.13.
🐍🍒⛏🤖

[miss-islington-app]

Sorry, @AlexWaygood, I could not cleanly backport this to 3.13 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker 0d9d56c4e4246495f506f7fb319548fb105b535b 3.13

[miss-islington-app]

Sorry, @AlexWaygood, I could not cleanly backport this to 3.12 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker 0d9d56c4e4246495f506f7fb319548fb105b535b 3.12