Export types required to use slots

[hosmelq]

I exported certain utilities that are needed to use the slots feature, as I intend to utilize them in my custom components.

✅ Pull Request Checklist:

• Included link to corresponding React Spectrum GitHub Issue.
• Added/updated unit tests and storybook for this change (for new code or code which already has tests).
• Filled out test instructions.
• Updated documentation (if it already exists for this component).
• Looked at the Accessibility Practices for this feature - Aria Practices

📝 Test Instructions:

🧢 Your Project:

[reidbarber]

Thanks! Feel free to sign the CLA, and close and re-open the issue, then the build should pass.