TreeView: Add accessible names to `LeadingVisual`

[TylerJDev]

Closes https://github.com/github/primer/issues/3444

Changelog

New

• Adds accessible names (aria-label) to leading visuals in TreeView story
• Adjusts "Without Indentation" story based on feedback

Rollout strategy

• [ ] Patch release
• [ ] Minor release
• [ ] Major release; if selected, include a written rollout or migration plan
• [x] None; if selected, include a brief description as to why (Storybook specific)

Testing & Reviewing

Merge checklist

• [ ] Added/updated tests
• [ ] Added/updated documentation
• [x] Added/updated previews (Storybook)
• [ ] Changes are SSR compatible
• [x] Tested in Chrome
• [ ] Tested in Firefox
• [ ] Tested in Safari
• [ ] Tested in Edge
• [ ] (GitHub staff only) Integration tests pass at github/github (Learn more about how to run integration tests)

[changeset-bot[bot]]

⚠️ No Changeset found

Latest commit: 4099a779bf3937fca590fb8783d53b32f0de2ade

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[github-actions[bot]]

size-limit report 📦

Path	Size
packages/react/dist/browser.esm.js	96.32 KB (0%)
packages/react/dist/browser.umd.js	96.65 KB (0%)