Fix movementX and movementY properties of mouse events

Calculate movementX/movementY at every turn, not only when
the mouse is in locked state.

Task-number: QTBUG-59127
Change-Id: I362e055e6b5d6f831671604a093434373cedf19a
Reviewed-by: Peter Varga <pvarga@inf.u-szeged.hu>
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>