docs: replace vite-plugin-stylex-dev with stylex-extend

[BeiyanYunyi]

What changed / motivation ?

This PR changes the documentation of third-party bundler integrations.

According to vite-plugin-stylex-dev's document, it is no longer maintained, and the author encourage us to use stylex-extend by the same author instead.

Linked PR/Issues

Additional Context

Pre-flight checklist

• I have read the contributing guidelines
  Contribution Guidelines
• Performed a self-review of my code

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