Requests that this Node get the input focus, and that this Node's top-level ancestor become the focused window. To be eligible to receive the focus, the node must be part of a scene, it and all of its ancestors must be visible, and it must not be disabled. If this node is eligible, this function will cause it to become this Scene's "focus owner". Each scene has at most one focus owner node. The focus owner will not actually have the input focus, however, unless the scene belongs to a Stage that is both visible and active.