Idea: Use https://github.com/openglonmetal/MGL to support OpenGL 4.3 on macOS

[UltraHDR]

[SleepingSnakezzz]

That isn't how that project works. It converts OpenGL 4.6 calls into Metal calls. Citra currently uses OpenGL 4.3, and work for a Vulkan backend is already underway. Once that is completed, we'll look into getting MacOS support back on track.