`getItemKey` is called with invalid index

[lesha1201]

Describe the bug

getItemKey might be called with an index which is out of range of the current count . It can happen because ResizeObserver might be called with the previous nodes and new nodes after the list is changed. For example,

[
  <previous-node data-index="0" />,
  <previous-node data-index="1" />,
  <new-node data-index="0" />,
]

Previously, we were checking if there is an item with such index in measurementsCache but now we don't check it and because of that getItemKey is called with a wrong index.

https://github.com/TanStack/virtual/pull/521/files#diff-85d1b85f3d4e501779ca41e51cd38cf7f61a2b7ffddaf958cd7e79c2787c36f1L564-L569

Expected behavior

Not sure what's the right behavior. I guess we should call this.observer.unobserve(node) for the previous nodes here and at the same time to not call getItemKey with the previous indexes.

I can accomplish this partially by falling back to an index in getItemKey, e.g.:

const getItemKey = (index) => data[index]?.key || index

In this case it will unobserver the previous nodes. But I'm not sure if it's intended way of using getItemKey and it doesn't clear measureElementCache (this.measureElementCache.delete(elementKey)).

tanstack-virtual version

v3.0.0-beta.59

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