Possible FocusZone logic error #4317

FocusOutsideZone(..., forward=false) starts from PreOrderPrevious(container), but when the FocusZone has no previous sibling, PreOrderPrevious(container) returns the parent. Calling FindLastFocusableElement(parent) then searches the parent's entire descendant subtree, which can select an element inside this FocusZone or a later sibling after it, so Shift+Tab can re-enter the zone or jump forward instead of moving to the previous element outside the zone.

Please fix the backward traversal to skip the FocusZone subtree and later siblings: when there is no previous sibling, consider the parent itself or keep climbing to the parent's previous sibling. Add a native focus traversal test for a FocusZone that is the first child and has later siblings.

Internal link: https://office.visualstudio.com/DefaultCollection/Office/_git/Office/pullRequest/5751726?discussionId=73697562#1790023382