Bug: use keyToListDimensionsMap instead of indexKey to find item dimension first.

[ryuever]

To Reproduce

const useMountItem = props => {
  if (initialRef.current) {
    const { remover, dimensions: itemDimensions } = dimensions.registerItem(
      itemKey,
      {
        ignoredToPerBatch,
        recyclerType,
      },
    );
    disposerRef.current = remover;
    // @ts-ignore
    itemDimensionsRef.current = itemDimensions

    initialRef.current = false;
  }

  useMemo(() => {
    // itemMeta will be null
    const itemMeta = dimension.getFinalKeyMeta(itemKey)
  }, [])
}