chore(react-router): cleanup test setup

[MichaelDeBoey]

These are all available in Node 20 (which is the minimum we use)

Since we're still using jest and jest-environment-jsdom we unfortunatelly can't fully remove these 😢

Decided to go with @kettanaito / @mswjs' jest-fixed-jsdom though as it's handling more cases than we currently do and it's one less thing we need to worry about ourselves

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[kettanaito]

Just bear in mind that jest-fixed-jsdom is largely a hack and shouldn't be used as a long-lasting solution.

If you can, please explore migrating your tests to run in the browser (Browser Mode in Vitest, Component testing in Playwright and Cypress). Much simpler setup, much better tests, but you need to pay some attention migrating.