Fix useTreeData subtree move validation

[su-jin1425]

Description

Closes #10539

Summary

Prevent useTreeData from silently dropping nodes when an item is moved into its own subtree.

This adds validation to the imperative move, moveBefore, and moveAfter APIs so that moves targeting a node's own descendants throw:

Cannot move an item to be a child of itself.

The validation also covers root-level nodes, which were previously missed by moveBefore and moveAfter.

Changes

• Added ancestor validation to move().
• Fixed root-level ancestor validation in moveBefore() and moveAfter().
• Added isolated regression tests covering nested and root-level self-subtree moves for all three APIs.
• No changes to drag-and-drop behavior.

Pull Request Checklist:

• Included link to corresponding [React Spectrum GitHub Issue](useTreeData: move() silently drops a node moved into its own subtree; moveBefore/moveAfter miss root-level nodes #10539).
• 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](https://www.w3.org/WAI/ARIA/apg/).
• I understand every change in this PR and can explain why it's there.
• If AI-assisted, I followed our [AI contribution guidance](https://github.com/adobe/react-spectrum/blob/main/CONTRIBUTING.md#ai-assisted-contributions) and pointed my assistant at https://github.com/adobe/react-spectrum/blob/main/CLAUDE.md.

Test Instructions:

Run the useTreeData test suite:

yarn jest useTreeData

The regression tests verify that move, moveBefore, and moveAfter throw when attempting to move an item into its own subtree, including root-level ancestor cases.

Your Project:

None

[snowystinger]

I see, change it to this:

    let reactMajor = parseInt(React.version, 10);
    let expectMoveError = (result, action) => {
      if (reactMajor >= 18) {
        expect(() => act(action)).toThrow('Cannot move an item to be a child of itself.');
      } else {
        act(action);
        expect(result.error?.message).toContain('Cannot move an item to be a child of itself.');
      }
    };

and put the change I made to source back or explain why it doesn't work

[su-jin1425]

Thanks for the cleaner test helper! I've updated the tests to use expectMoveError.

My previous commit reverting your while (parent != null) logic was just an accidental git staging mistake while debugging locally.

[su-jin1425]

When I saw Ci fail I suspected your change to the while loop in useTreeData.ts might have caused it.
To test this theory, I ran git checkout aef9f68 packages/react-stately/src/data/useTreeData.ts to see if it fixed the test failures locally. eventually figured out the actual issue was a yarn cache problem locally However, I forgot to un-stage my temporary checkout of useTreeData.ts. So when I committed the test fixes

Thank you for correcting me.