[Docs] Explanation: Form Resubmissions and Data Validation

[brookslybrand]

Describe what's incorrect/missing in the documentation

Drawing from Remix's resubmission guide, we need to document how to handle form resubmissions and data revalidation in React Router, including best practices for managing the user experience during these scenarios.

[brookslybrand]

This could maybe repurpose the revalidations section of the remix.run Single Fetch doc as well