PressAndHold make drag target jump

This was seen with QML compiled from qt/qt-qml HEAD at
89d40b78597aec3ecf39ad8e2dd84427bc48dc73 and
tesla HEAD at d60b35fe01620f7caec77afae891600116223f23

Open the launcher screen with icon grid. Click on one of the icons and drag very slightly
vertically. Wait till the PressAndHold timeout has passed (i.e. 700ms), then drag again
slowly. Note how often the icon jumps off when the second drag starts, so that it is no longer
under the mouse pointer (the amount it jumps seems random from icon to icon, sometimes
it jumps off the screen entirely, but it usually jumps towards the upper right corner of the screen).