touchpad: always reset the motion history on finger changes

touchpad: always reset the motion history on finger changes

We've already been doing this for semi-mt devices and for non-clickpads but
let's do it for clickpads as well. On Synaptics touchpads (PS/2 and RMI4)
we see slot jumps where two slots are active, slot X ends but slot Y continues
with the other slot's positional data. This causes a cursor jump on finger
lift after a two-finger scrolling motion. Simply resetting the motion history fixes it.

The only multi-finger interaction where a user could expect perfect fluid
motion is when using a second finger to touch cone of the software button
areas. Let's see if we have complaints first before we implement something
more complex.

https://bugs.freedesktop.org/show_bug.cgi?id=91695

Signed-off-by:Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>