wayland: Scale smooth scroll events to pointer motion coordinate space

Smooth scroll event vectors from clutter have the same dimensions as the
ones from from Xi2, i.e. where 1.0 is 1 discrete scroll step. To scale
these to the coordinate space used by wl_pointer.axis
vertical/horizontal scroll events, multiply the vector by 10.

https://bugzilla.gnome.org/show_bug.cgi?id=729601