fix: focus restoring in collections

[snowystinger]

Closes

As an alternative to #9539

✅ Pull Request Checklist:

• Included link to corresponding React Spectrum GitHub Issue.
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• 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:

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[devongovett]

I'm a little worried about the performance of traversing two collections. Maybe there's a simpler algorithm we can use where we walk the old collection starting from the focused key until we find an item that exists in the new collection. Though if the items were also re-ordered at the same time as items were removed the results could be unexpected. How much do we care about that case?

[devongovett]

I think with new collections startItem.index will be relative to the section, not the entire list so this comparison may not work. It would also not account for non-item siblings which would affect its index.