Not all mice have a click angle with integer degrees. The new
MOUSE_WHEEL_CLICK_COUNT property specifies how many clicks per full rotation,
the angle can be calculated from that.
See https://github.com/systemd/systemd/pull/4440 for more information
CLICK_COUNT overrides CLICK_ANGLE, so we check for the former first and then
fall back to the angle if need be. No changes to the user-facing API.
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
