Fix mouse wheel scrolling with libinput

If the Libinput X server input driver is used we get a value for
pixelDelta for a physical mouse wheel scroll, so we check that the
source of the wheel event is actually a mouse, this was fixed in
Qt 5.9.5
https://bugreports.qt.io/browse/QTBUG-59261

Patch by ahmadsamir

BUG: 386762
Differential Revision: https://phabricator.kde.org/D9008