Add support for high-resolution wheel scrolling

[emersion]

See:

• https://lists.freedesktop.org/archives/wayland-devel/2019-January/039901.html
• https://who-t.blogspot.com/2018/12/high-resolution-wheel-scrolling-on.html

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wlroots has migrated to gitlab.freedesktop.org. This issue has been moved to:

https://gitlab.freedesktop.org/wlroots/wlroots/-/issues/1508