Export LocalizedStringFormatter type in React-Aria

[alexasselin008]

Closes #6013

I created this PR before the issue was discussed with the maintainers, so feel free to discuss this proposed type export either on this PR or on the related issue.

✅ 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

[LFDanLu]

This seems fine to me, think it might just be something we may have missed exporting when switching from useMessageFormatter to useLocalizedStringFormatter. Thanks!