fix: refactor useTreeData

[reidbarber]

Testing to see if this fixes some of the issues found in testing. We'll need to add test cases for the issues we were observing.

✅ 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:

[rspbot]

Build successful! 🎉

• View the storybook
• View the storybook-19
• View the storybook-17
• View the storybook-16
• View the S2 storybook
• View the documentation

[rspbot]

Build successful! 🎉

• View the storybook
• View the storybook-19
• View the storybook-17
• View the storybook-16
• View the S2 storybook
• View the documentation

[rspbot]

## API Changes

@react-stately/data

/@react-stately/data:TreeData

 TreeData <T extends {}> {
   append: (Key | null, Array<{}>) => void
+  getDescendantKeys: (TreeNode<{}>) => Array<Key>
   getItem: (Key) => TreeNode<{}> | undefined
   insert: (Key | null, number, Array<{}>) => void
   insertAfter: (Key, Array<{}>) => void
   insertBefore: (Key, Array<{}>) => void
   move: (Key, Key | null, number) => void
   moveAfter: (Key, Iterable<Key>) => void
   moveBefore: (Key, Iterable<Key>) => void
   prepend: (Key | null, Array<{}>) => void
   remove: (Array<Key>) => void
   removeSelectedItems: () => void
   selectedKeys: Set<Key>
   setSelectedKeys: (Set<Key>) => void
   update: (Key, {}) => void
 }

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