main/postmarketos-ui-plasma-mobile: follow upstream in kdeglobals, lower StartDragDist (MR 2937)

Follow upstream change in https://invent.kde.org/plasma-mobile/plasma-phone-settings/-/blob/master/etc/xdg/kdeglobals
Lower StartDragDist so that flicks feel smoother (less "jumping" when a flick gesture is detected).