Add package pythreejs

[mkoeppe]

... and two dependencies. All 3 packages are installed as platform-independent wheels.

This hopefully can replace our custom threejs build. Fixes #32070

📝 Checklist

• The title is concise, informative, and self-explanatory.
• The description explains in detail what this PR is about.
• I have linked a relevant issue or discussion.
• I have created tests covering the changes.
• I have updated the documentation accordingly.

⌛ Dependencies

[github-actions]

Documentation preview for this PR (built with commit b94cf26; changes) is ready! 🎉