fix(dnd): dispatch focusin on cancel to fix keyboard nav with no drop targets

[reidbarber]

Closes #9495

✅ 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:

Test new story:

  1. Focus on an item's drag button
  2. Press Enter to start keyboard drag
  3. Notice there are no valid drop targets (shouldAcceptItemDrop rejects all item drops)
  4. Press Escape to cancel the drag
  5. Try pressing arrow keys
  6. Observe that focus moves (and we've exited virtual drag mode)

🧢 Your Project:

[rspbot]

Build successful! 🎉

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• View the S2 docs
• View the React Aria docs