touchpad: disable tapping for fingers exceeding the timeout/motion threshold

touchpad: disable tapping for fingers exceeding the timeout/motion threshold

The current code triggers multi-finger tapping even if the finger released was
previously held on the touchpad for a while. For an event sequence of:
1. first finger down
2. first finger move past threshold/wait past timeout
3. second finger down
4. first finger up

The second finger initiates the two-finger tap state, but the button event is
sent when the first finger releases - despite that finger not meeting the
usual tap constraints. This sequence can happen whenever a user swaps fingers.

Add the finger state to the actual touchpoints and update them whenever the
constrains are broken. Then, discard button events if the respective touch
did not meet the conditions.

http://bugs.freedesktop.org/76760

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