SliverAnimatedList constructor
      const
      SliverAnimatedList({ 
    
- Key? key,
 - required AnimatedListItemBuilder itemBuilder,
 - ChildIndexGetter? findChildIndexCallback,
 - int initialItemCount = 0,
 
Creates a sliver that animates items when they are inserted or removed.
Implementation
const SliverAnimatedList({
  Key? key,
  required this.itemBuilder,
  this.findChildIndexCallback,
  this.initialItemCount = 0,
})  : assert(itemBuilder != null),
      assert(initialItemCount != null && initialItemCount >= 0),
      super(key: key);