This functionality was only in Qt Quick in Qt 5. Now we move it up to QtGui
so that every QEventPoint will have a valid velocity() before being delivered
anywhere.
[ChangeLog][QtGui][QPointerEvent] Every QEventPoint should now carry a valid
velocity(): if the operating system doesn't provide it, Qt will calculate it,
using a simple Kalman filter to provide a weighted average over time.
Fixes: QTBUG-33891
Change-Id: I40352f717f0ad6edd87cf71ef55e955a591eeea1
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>