fix(xhr): clone request body before calculating its size

[kettanaito]

• Related to #2273
• Fixes #2279
• Latest release tag: https://github.com/mswjs/interceptors/releases/tag/v0.35.3

[kettanaito]

Released: v2.4.6 🎉

This has been released in v2.4.6!

• 📄 Release notes
• 📦 npm package

Make sure to always update to the latest version (npm i msw@latest) to get the newest features and bug fixes.

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