Differentiate between Animation targets list that is empty vs one that hasn't been defined

If you add items to the end of a list, there will be targetItems but no displacedItems (since no items will be displaced by the insertion). However this means the displacedItems animation requires

NumberAnimation { targets: displacedItems; exclude: targetItems }

instead of just

NumberAnimation { targets: displacedItems }

because the displacedItems list is empty, which means it will default to being applied to any matching object, i.e. the targetItems, and so the displacedItems animation will be applied to the targetItems.