With Qt5 QCursor does no longer provide ::handle() which was used to
set a cursor on a native XWindow for which we do not have a QWidget.
Also KWin has had for quite some time an optimized version to get the
cursor position without doing XQueryPointer each time ::pos() is called.
These two features are merged into a new class Cursor providing more or
less the same API as QCursor.
In addition the new class provides a facility to perform mouse polling
replacing the implementations in Compositor and ScreenEdges.
For more information about the new class see the documentation for the
new class in cursor.h.
