HID: wacom: Add additional tests of confidence behavior

Test for proper driver behavior when the touch confidence bit is set
or cleared. Test the three flavors of touch confidence loss (tipswitch
cleared before confidence, tipswitch and confidence cleared at the same
time, and tipswitch only cleared when touch is actually removed). Also
test two flavors of touch confidence gain (confidence added to a touch
that was "never" confident, and confidence added to a touch that was
previously confident).

Signed-off-by: Jason Gerecke <jason.gerecke@wacom.com>
Signed-off-by: Jiri Kosina <jkosina@suse.com>