hwdb: add MOUSE_WHEEL_CLICK_ANGLE as property

hwdb: add MOUSE_WHEEL_CLICK_ANGLE as property

Most mice have a wheel click angle of 15 degrees, i.e. 24 clicks per full
wheel rotation. Some mice, like the Logitech M325 have a larger angle. To
allow userspace to make use of that knowledge, add a property to the hwdb.

This allows for better predictive scrolling. e.g. a mouse that has a smaller
click angle will scroll faster, with this value you can accommodate this
where needed. Likewise, using "half turn of the wheel" or "full turn of the
wheel" as a UI element becomes possible.

This addition is mainly driven by libinput 0.8, having the angle enables
libinput to provide an API that distinguishes between a physical distance
(like touchpad scrolling does) and discrete steps (wheel clicks).
Callers can choose what they prefer based on the device.