Fix csf-plugin loader

[valentinpalkovic]

Closes #21387

What I did

The CSF-Plugin loader was not applying the necessary transformations in Angular projects.

How to test

1. Run an Angular sandbox
2. Open Storybook in your browser
3. Access the addons-docs-docspage-basic--docs Story -> JSDocs should be visible

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.

["cleanup", "BREAKING CHANGE", "feature request", "bug", "documentation", "maintenance", "dependencies", "other"]

[shilman]

@valentinpalkovic @ndelangen did you test this change across various project types? When I wrote csf-plugin I originally wrote it as a transformer, but switched to a loader to make sure that the code it processes still contains comments. That wasn't the case at the time.

[valentinpalkovic]

@shilman I have written an e2e test that guarantees its functionality across all sandboxes. Or do you have a community project in mind, where it was not working?

[shilman]

@valentinpalkovic I don't actually remember the problem case, just that it was common. Perhaps these lines fix it. Let's consider it solved and see if anything comes back from the community. Thanks for testing!!! 🙏