Build: Rework test NPM script

[gaetanmaisse]

Applying #13559 step by step to not face gigantic conflicts or issues with the webpack 4/5 works.

What I did

Previously the unit tests were run with a custom script scripts/test.js.
This script was a kind of wrapper around Jest, handling just a few options (skipping all the unknown ones) and spawning Jest programmatically.
To simplify this process:

• I extracted the only non-classic case in its own NPM script: yarn test-puppeteer
• Just call Jest directly when running yarn test so all the options are forwarded properly to Jest.

⚠️ yarn test --core doesn't work anymore as --core isn't a Jest option, it is now simply yarn test. All the other options are still available:

• --watch
• --coverage
• --runInBand
• --w2 is now --> -w 2
• --reportLeaks is now --> --detectLeaks
• --update is now --> -u or --updateSnapshot

📝 We can now run the tests of a single workspace by simply use --projects, for instance: yarn test --projects examples/angular-cli

I also updated:

• The doc to replace all the mentions of yarn test --core by yarn test
• CI scripts, to use --runInBand --ci, for details see https://jestjs.io/docs/en/cli#--ci

How to test

• CI should be green and you should be able to run yarn test with any Jest option.

[phated]

Wow! Awesome! 🎊

[ghengeveld]

Omg my hero

[shilman]

🙌