Replace Carbon with ApplicationServices

[SRHMorris]

This is macOS only.

Rather than linking to the Carbon framework, I'm pretty sure you can just link to the ApplicationServices framework, and in SystemMonitor_macos.cpp replace the include with ApplicationServices/ApplicationServices.h. I think that's the only usage of Carbon anyway.

Similarly, linking to this framework (here) only needs to be done if OCIO_HEADLESS_ENABLED is not defined (on another note, I couldn't find if this is enabled by CMake, I've been enabling it manually by adding it to the compiler flags).

I could submit a PR, but it might take time to go through legal.

[doug-walker]

A PR would certainly be welcome @SRHMorris.