Core: Remove storiesOf-API

[ndelangen]

What I did

It's time.

The storiesOf-API has been around since forever, but it's major problem has always been the fact that defining stories using it needed the code to run in order for storybook to determine which stories to show in the sidebar, which creates a bi-directional dependence between manager & preview.

We've created CSF as a replacement for defining stories in/with. This has seen a few iteration/improvements/enhancements.

CSF is statically analyzable/extractable; which causes storybook to extract stories much much faster in NodeJS as it starts-up.
The other benefit is storybook can also lazy load stories as they are navigated to.

In Storybook 6.x we introduced storyStoreV7 as a feature-flag, which users could/would opt-in to to get much faster start-times, at the cost of it not supporting the storiesOf-API.
In Storybook 7.0 this feature-flag was inverted to be true by default.
And now in Storybook 8.0 we're removing the storiesOf-API entirely.

One of the remaining use-cases for storiesOf has been dynamically generating stories.

In Storybook 7 we've introduced an indexer API which solves this problem, in a different way.
In Storybook 8 that API has matured and been iterated upon. I won't go into details here.

So this is the end of the road for storiesOf.

Notes

This PR does not yet remove storyStoreV7 feature flag (yet). It does make that flag effectively broken by design.

I figured we could take the task of removing storyStoreV6 support step by step, starting with this (the most public) one.

Checklist for Contributors

Testing

The changes in this PR are covered in the following automated tests:

• stories
• unit tests
• integration tests
• end-to-end tests

Manual testing

TBD

Documentation

!!! TODO !!!

Checklist for Maintainers

• When this PR is ready for testing, make sure to add ci:normal, ci:merged or ci:daily GH label to it to run a specific set of sandboxes. The particular set of sandboxes can be found in code/lib/cli/src/sandbox-templates.ts

• Make sure this PR contains one of the labels below:

  Available labels

  • bug: Internal changes that fixes incorrect behavior.
  • maintenance: User-facing maintenance tasks.
  • dependencies: Upgrading (sometimes downgrading) dependencies.
  • build: Internal-facing build tooling & test updates. Will not show up in release changelog.
  • cleanup: Minor cleanup style change. Will not show up in release changelog.
  • documentation: Documentation only changes. Will not show up in release changelog.
  • feature request: Introducing a new feature.
  • BREAKING CHANGE: Changes that break compatibility in some way with current major version.
  • other: Changes that don't fit in the above categories.

🦋 Canary release

This PR does not have a canary release associated. You can request a canary release of this pull request by mentioning the @storybookjs/core team here.

core team members can create a canary release here or locally with gh workflow run --repo storybookjs/storybook canary-release-pr.yml --field pr=<PR_NUMBER>