Almost all non Apple touchpads have visible markings for software button areas,
so limit clickfinger behavior to Apple clickpads, and implement software button
areas for others.

This is a slightly fancier implementation than the simplest model and ported
over from libtouchpad. It implements a state machine for the software buttons
with left and right buttons currently implemented. Buttons are oriented
left-to-right, in a horizontal bar. No random button placement allowed.

In general, the procedure is:
- if a finger sets down in the left button area, a click is a left click
- if a finger sets down in the right button area, a click is a right click
- if a finger leaves the button area, a click is a left click
- if a finger starts outside the button area, a click is a left click

Two timeouts are used to handle buttons more smoothly:
- if a finger sets down in a button area but "immediately" moves over
  to a different area, that area takes effect on a click.
- if a finger leaves a button area and "immediately" clicks or moves back into
  the area, the button still takes effect on a click.
- if a finger changes between areas and stays there for a timeout, that area
  takes effect on a click.

Note the button area states are named BOTTOM_foo to make it easier to later
add support for a top button area such as can be found on the Thinkpad [2-5]40
series.

Co-authored-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Jonas Ådahl <jadahl@gmail.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>