Core: Improve project root detection logic

[dobesv]

• Support .hg
• Support .yarn
• Support an env var STORYBOOK_PROJECT_ROOT as an override if other detection methods are not working

Issues: #20314 #14042 #20211

What I did

Update getProjectRoot logic to cover additional use cases.

How to test

See the related issues for the cases that lead to this.

Checklist

• Make sure your changes are tested (stories and/or unit, integration, or end-to-end tests)
• Make sure to add/update documentation regarding your changes
• If you are deprecating/removing a feature, make sure to update
  MIGRATION.MD

Maintainers

• If this PR should be tested against many or all sandboxes,
  make sure to add the ci:merged or ci:daily GH label to it.
• Make sure this PR contains one of the labels below.

[kylegach]

Hey, @dobesv! Thank you for this contribution (and congratulations on your first!). Could you add some tests for this, please?

[dobesv]

Any pointers on how and where to add the tests? I'm not too familiar with the project, and I don't think there are existing tests for this function unfortunately. It seems a bit tricky to test.

[ndelangen]

I left 2 comments

[ndelangen]

@dobesv thank you for contributiong! I think this change is good, but I'd like it implemented in a slightly different way, I hope you can make that happen? 🙏

[dobesv]

Thanks for the review @ndelangen . I made changes based on your feedback. If you have any thoughts about how I could make automated tests for this without a ton of work, let me know.

[ndelangen]

We could add tests that mock find-up; that would mean we only have to specify when find-up with returns with what string..