[jest] refactor config check

[spalger]

We received a report from the core team that some of their tests were executing multiple times. This lead to discovering that the current config check improperly required that config files were included in places where they are not needed, causing many test files to be tested twice on CI.

The issue stems from an attempt to be helpful and tell contributors where config files should live. Unfortunately, as things have changed and we have needed to split up jest configs, this logic grew incorrect. I've tried to fix it several times but I'm tired of trying to make it work and don't think that jest config creation is something most people need a lot of help with anymore (especially once we get to packages for all the things).

This PR reworks that check to flip the logic around a bit, find all the jest test and config files in the repo, then use Jest APIs to determine the list of test files for each Jest config. Any test that isn't selected by a jest config will produce an error, and any test file that is selected by multiple configs will also produce an error.

IMO this is a much simpler thing to write correctly, and the logic seems sound to me for now.

Gist of the errors found by this PR before deleting config files: https://gist.github.com/spalger/be739eb4290756df4be83dd6b5410d51

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Status	Branch	Result
❌	8.3	Backport failed because of merge conflicts You might need to backport the following PRs to 8.3: - Bump Node.js to 16.16.0 (#135926)

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