Some mice have an additional horizontal scroll wheel. This patch adds support
for receiving such events. By default it is used to scroll 2D editors left and right.
I originally developed this because I was missing it in the spreadsheet, but it
seems to be useful in many other editors too.
It's supported on Linux (Wayland), Windows and macos.
Pull Request: https://projects.blender.org/blender/blender/pulls/138758
afd760f2b7