wayland: Add support for high resolution scrolling

In libinput 1.19, three new pointer axis events were added in order to
provide support for high-resolution scrolling.

LIBINPUT_EVENT_POINTER_AXIS is de-facto deprecated and new users of
libinput should use instead SCROLL_WHEEL, SCROLL_FINGER, and
SCROLL_CONTINUOUS.

Discrete deltas were replaced with v120 delta values. 120 corresponds to
a single discrete delta. Smaller values correspond to "partial" wheel
ticks.

https://gitlab.freedesktop.org/wayland/wayland/-/merge_requests/72