Horizontal scrolling not working on macOS because of shift handling

[ptxmac]

Version/Branch of Dear ImGui:

Version: 1.83
Branch: master

Back-end/Renderer/Compiler/OS

Back-ends: imgui_impl_opengl3.cpp + imgui_impl_glfwcpp
Compiler: clang
Operating System: macOS 11.2.3

My Issue/Question:

Imgui has a feature to allow the shift key to flip between horizontal/vertical scrolling: https://github.com/ocornut/imgui/blob/master/imgui.cpp#L3757

Unfortunately, this conflicts with macOS's built-in feature which does the same.

When holding down shift while scrolling on macOS, the system sends horizontal events, but imgui also detects the shift key, and only look at the vertical events - effectively disabling horizontal scrolling!

Standalone, minimal, complete and verifiable example:

Run any example (tested with sdl and glfw) that contains a horizontal scrollbar (e.g. demo menu / examples / log)

Suggested fix

Add an option to disable the shift scrolling override feature

[ocornut]

Pushed a fix for this (92b7b1f, slightly different from 2b0090c initially pushed).

I tried a magic mouse (with support for swiping on both axis) and Shift didn't affect either, so I presume it only affect something on mouse that only have a single axis.
I installed drivers to try a magic mouse on my Windows and Shift altered the vertical wheel into horizontal scroll, but didn't alter horizontal wheel into vertical scroll.

Should be fixed.

We'll be looking at #3795 next