Fix react-router-dom main entry metadata

[leo1987820]

Summary

• point react-router-dom's CommonJS main field at the packaged ./dist/index.js file
• add a patch change file for the package metadata fix

Verification

• Confirmed react-router-dom@7.18.0 currently declares main: "./dist/main.js" on npm.
• Confirmed the published tarball does not contain package/dist/main.js.
• Confirmed the published tarball contains package/dist/index.js and package/dist/index.mjs.
• Confirmed this branch only changes packages/react-router-dom/package.json and adds the package change file.

[remix-cla-bot]

Hi @leo1987820,

Welcome, and thank you for contributing to React Router!

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Thanks!

- The Remix team

[remix-cla-bot]

Thank you for signing the Contributor License Agreement. Let's get this merged! 🥳

[brophdawg11]

Thanks!