/// Internal implementation of CreateRootPopup to allow tooltips to
/// Internal implementation of CreateRootPopup to allow tooltips to
/// override the popup's placement in case the tooltip comes from keyboard focus.
/// </summary>
/// <param name="popup">The parent popup that the child will be hooked up to.</param>
/// <param name="child">The element to be the child of the popup.</param>
/// <param name="bindTreatMousePlacementAsBottomProperty">Whether to bind TreatMousePlacementAsBottomProperty to the child's FromKeyboard property</param>