touchpad: work thumb detection into the tap state machine

touchpad: work thumb detection into the tap state machine

Most thumbs are detected a few events into the sequence. Work this into parts
of the tapping state machine. Only the most common use-case is handled here -
if the first finger ends up being marked as a thumb, we return to the idle
state and ignore that touch sequence.

At any other state, we handle thumbs like any other finger.

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