Add macOS platform support

[mcayland]

Now that Linux platform support has been merged, it shouldn't be too difficult to add support for the macOS platform (along with corresponding CI workflows to ensure that the macOS platform build doesn't break).

[clhin]

It would be nice to have a short guide on how to go about building even if it can't compile yet. I'm not sure which presets to use to get it to a point where I can compile it and I would like to make an attempt.

[benstone]

If you'd like to try building on macOS, you should be able to get started by running cmake followed by cmake --build, similar to the Linux build instructions in the README. The build presets currently set the build configuration, install directory and the 3DMM_GUI option. The 3DMM_GUI option will be automatically set to SDL on non-Windows systems. While the Linux presets have "Linux" and "x86_64" in the name, they don't actually specify the platform or architecture, so they should work on macOS too.