Before this change, it was possible to move the focus onto a control that was no longer in the view using focus traversal. This changes that, so that when a control is focused, it makes sure that if it is the child of a scrollable, that the scrollable attempts to keep it in view. If it is already in view, then nothing scrolls.

When asked to move in a direction, the focus traversal code tries to find a control to move to inside the scrollable first, and then looks for things outside of the scrollable only once the scrollable has reached its limit in that direction.