Focuses the next widget in the given
direction in the focus scope that
contains the given
This should determine what the next node to receive focus in the given
direction should be by inspecting the node tree, and then calling
FocusNode.requestFocus on the node that has been selected.
Returns true if it successfully found a node and requested focus.
All arguments must not be null.
bool inDirection(FocusNode currentNode, TraversalDirection direction);