libobs: Update macOS platform implementation

Cleans up the source code by sorting functions by topic and also
removes macros for hotkey implementation, removing the need to disable
compiler warnings.

Key codes and descriptions are now contained in arrays which either
use the OBS key code or the macOS key code as lookup keys with all
necessary context information directly associated with the key.

The implementation also uses the zero-initialization rule for arrays
of structs in such a way that the struct's "is_valid" boolean is
"false" by default so that only values explicitly initialized with a
key are ever "valid".