#13727 - sketch - stroke - swiping over stroke skyle selects it

[Zeljko-Predjeskovic]

Fixed action sheet returning the wrong item on touch and selecting while scrolling

• The item tap handler called AcceptPrimary() without ever setting SelectedItem.
  ListBox selects on PointerReleased for touch and pen, not on press, so the
  handler ran before the selection updated and GetResult() returned the
  previously selected item.
• Any press+release on the same item counted as a tap, so flicking the list to
  scroll it accepted whatever item the finger happened to land on.
• The tapped item is now resolved from the item visual's DataContext and assigned
  to SelectedItem before AcceptPrimary(), instead of trusting ListBox.SelectedItem.
• A tap is cancelled either when the pointer travels further than
  IPlatformSettings.GetTapSize, or when a gesture recognizer steals the pointer
  (PointerCaptureLost). Both are needed: ScrollGestureRecognizer only tracks
  touch/pen, so mouse click-drags rely solely on the tap-slop check, and it bails
  out at the scroll boundaries, so overscroll drags never trigger a capture loss
  either. Conversely a normal touch scroll starts at half the tap size, so it
  cancels via capture loss before the slop check would fire.
• Removed the dead SelectingItemsControl_OnSelectionChanged and
  InputElement_OnKeyUp handlers - neither was wired up in the axaml. Enter and
  Escape are still handled by InputElement_OnKeyDown.