Mention `node-polyfill-webpack-plugin` in the Language Support docs

[jtpio]

The docs mention @rspack/plugin-node-polyfill here: https://www.rspack.dev/guide/language-support#node-polyfills

However it looks like that package has now been deprecated:

• https://github.com/web-infra-dev/rspack/pull/4937
• https://github.com/web-infra-dev/rspack/tree/main/packages/rspack-plugin-node-polyfill
• https://www.npmjs.com/package/@rspack/plugin-node-polyfill

This PR updates the docs to reflect that change, and encourage folks to use node-polyfill-webpack-plugin directly.

[netlify[bot]]

👷 Deploy request for rspack pending review.

Visit the deploys page to approve it

Name	Link
🔨 Latest commit	b3a48fe56b82bd6dda313e9ab2aa637e3c001a99

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[hardfist]

thanks