gdk/events: Add constructor for high-resolution scroll events

gdk/events: Add constructor for high-resolution scroll events

Starting with Linux Kernel v5.0 two new axes are available for
mice that support high-resolution wheel scrolling: REL_WHEEL_HI_RES and
REL_HWHEEL_HI_RES.

Both axes send data in fractions of 120 where each multiple of 120
amounts to one logical scroll event. Fractions of 120 indicate a wheel
movement less than one detent.

The 120 magic number is a copy of the Windows API, so this new
constructor can be used both in Linux >= 5.0 and Windows >= Vista.