The TreeViewState contains serializable state information for the TreeView.
This is primarily state that the user could have changed by interacting with the TreeView, for example the selection state, expanded state, navigation state and scroll state.
The TreeViewState is the only state that should be serialized/deserialized in the TreeView. The TreeView itself is not serializable and should be reconstructed from the tree data it is representing.
All the state contained in this class is updated by the TreeView itself. Access to this state can also be done through the TreeView API.