Resetting the motion history has the side-effect of swallowing movements, we
don't calculate deltas until we have 4 motion events. During a finger release,
we're likely to get a large pressure change between two events, resetting the
motion history prevents the cursor from jumping on release.

The value of 7 found by trial-and-error, tested on the T440 and T450 hardware.
The absolute value is highly variable but recordings show that the pressure
changes only by 1 or 2 units during normal interaction. Higher pressure
changes are during finger position changes but since those should not cause a
jump anyway, we tend to win there too.

Currently only enabled for negative pressure changes, let's see how we go with
that. This is enabled for all touchpads now, but the value may need
device-specific thresholds in the future.

https://bugs.freedesktop.org/show_bug.cgi?id=94379



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