DragHandler::cursorShape is flickering on the edges

The cursorShape property is very unreliable, at least on Linux. No matter which graphics system is used (X11/Wayland), the cursor on the far right and bottommost pixel edges of a dragged item is going to flicker a lot along the way.

This is probably due to the asynchronous nature of the windowing systems interaction with applications. But somehow global drag&drop does not flicker that bad when you, for example, drag a file item around the desktop.