Inline tests for integration/react-18

[eps1lon]

... and move it to react-current-version in preparation of #65058

If you want to split tests, create a separate .test file so that it's easy to find where a (failing) test is located.

There's more wrong with this test with regard to cleanup but I'm not digging into that now.

Closes NEXT-3262

[ijjk]

Stats from current PR

Default Build

General

	vercel/next.js canary	vercel/next.js sebbie/inline-tests	Change
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build cache

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Diff details

Diff for edge-ssr.js

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Commit: 4dfd98f

[huozhi]

Maybe we can make it a e2e test and specify the version? And we can test both 18 and 19 beta?

[eps1lon]

Are we planning to support 18 and 19 in Next.js?

[timneutkens]

Maybe migrate these to test/e2e and use nextTestSetup to isolate them?

[eps1lon]

Do we have a project that's tracking that instead? I'm trying to land the React sync and don't want to get side-tracked in big refactoring projects.