[Feature Request] Multi-mouse support for macOS

[mittonk]

https://docs.libretro.com/guides/input-controller-drivers/

shows multi-mouse support for Linux udev and Windows raw... but nothing for macOS.

RetroArch is currently using Cocoa API and HID Manager.

For comparison, https://github.com/icculus/manymouse supports multi-mouse on Macs using the older Carbon API and HID Manager. (A quick test indicates that works in Cocoa as well.)

(I've been able to use manymouse in libretro-dice to get basic functionality, but have too many multi-thread double-free and crash-on-exit issues to make that production code --- so integrating multi-mouse into the RetroArch input driver might scale better.)