[Workers] Improve TanStack Start Guide

[RndUsername]

Summary

Added:

• link to example for using TanStack Start with Solid instead of React
• show that @tanstack/react-start/server-entry does not need to be the worker entry (I had a hard time to find out how to add Durable Object classes)

Documentation checklist

• Is there a changelog entry (guidelines)? If you don't add one for something awesome and new (however small) — how will our customers find out? Changelogs are automatically posted to RSS feeds, the Discord, and X.
• The change adheres to the documentation style guide.