Vitest plugin: Fix renamed export stories

[shilman]

Closes #29244

What I did

1. Save the local name of export variables in the CsfFile parsed output
2. Use that local name to fix the generated code in the Vitest plugin

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

In a sandbox, create a story that uses a renamed export and verify that the Vitest test succeeds. (I did not test!)

🦋 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>

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Greptile Summary

This PR adds support for renamed exports in the Storybook Vitest plugin, addressing issue #29244.

• Added localName property to StaticStory interface in CsfFile.ts to store original variable names
• Modified transformer.ts to use localName when generating test statements for renamed exports
• Updated CsfFile.test.ts to include tests for the new localName property
• Added a new test case in transformer.test.ts to verify handling of renamed exported stories

[greptile-apps]

LGTM

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[yannbf]

Thanks! Changes look good, but I found a bug in CsfFile (which could be done in a separate PR) where the story names are not handled in reexported consts like so:

const B = () => {}  
B.storyName = 'Custom name B'

const C = {
  name: 'Custom name C'
}
// story name is still B and D, should be "Custom name ..." for each story
export  { B, C as D }