* Move unit tests to one folder
* Migrate unit tests to TypeScript
* add test types to lint
* Ensure ts(x) tests are run with util
* Add tsx extension to jest config
* bump
This updates our `jest` configuration to no longer use `babel-jest` and instead uses `@swc/jest` which is much faster. This also updates to the latest version of `jest`, fixes our `tsconfig.json` used for tests (previously types in `node_modules` weren't resolved correctly), and ensures `next/dist` isn't un-necessarily transpiled in `jest`.
Timings for `yarn testheadless test/unit/` on CI
- before: 3m 30s - 4m ([example run](https://github.com/vercel/next.js/runs/3394701995))
- after: under 1m ([example run](https://github.com/vercel/next.js/pull/28400/checks?check_run_id=3395161621))
Timings for `yarn testheadless test/unit/` locally on m1 mac
- before: 90.16 seconds
- after: 29.92 seconds
