POC - SliverAnimatedListView

[AlexDochioiu]

Would be good to allow users to directly use the sliver list too.

This PR is a POC. It's probably best for AnimatedListView to become stateless and use SliverAnimatedListView internally.

[FriesI23]

Any updates on this PR?

The exposed widgets all wrapped with CustomScrollView right now, which kind of limits flexibility. Maybe we could expose ReorderableAnimatedListImpl directly.

Found that it has already been added to lib export

//Direct access to the sliver builder, circumventing the ScrollView layer
export 'src/builder/reorderable_animated_list_impl.dart';