Hidden: rename prop on -> when and reformat stories and add e2e tests

[broccolinisoup]

Renames the prop from being on -> when as discussed with the team on React Eng Sync. Because Hidden is a draft component, it is okay to release this as minor.

Also reformats the storybook and addes e2e tests.

For reformatting, the tracking issue: https://github.com/github/primer/issues/1488

Add storybook stories for Hidden

Checklist

• Ensure your chosen component has a component directory in the src directory
• Ensure the component has a root story file in the component directory
• Ensure that the root story file exports a Default story
• (Optional) Create a Playground story
• Move all other stories for the component into a .features.stories.tsx file
• Opt the component into storybook tests
• (Optional) Create visual regression tests for the component

[changeset-bot]

🦋 Changeset detected

Latest commit: e9309cf

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@primer/react	Minor

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[github-actions]

size-limit report 📦

Path	Size
dist/browser.esm.js	94.68 KB (0%)
dist/browser.umd.js	95.25 KB (0%)