This property controls whether the list view displays a header, in the form of a foldout that can be expanded or collapsed.
The default value is false.
When this property is set to true, Unity adds a foldout in the hierarchy of the list view and moves
the scroll view inside that newly created foldout. You can change the text of this foldout with headerTitle
property on the ListView.
If showBoundCollectionSize is set to true, the header includes a TextField to control
the array size, instead of using the field as part of the list.
If the makeHeader callback is set, no Foldout is shown.