Fixes T60682
Currently in the File Browser, symlinks are supported but not aliases(which are GUI friendly). So this patch adds that support. Carbon API has been Deprecated, so Foundation is being used. All methods are supported for > macOS 10.10.
The folder icon for redirection was added by D6816
Currently if I open "fake", it goes to "original" folder. Clicking back arrow brings me back to Desktop; directory up arrow takes me to Downloads. There doesn't seem compelling need to allow opening blender files via aliases, or adding scripts etc. Only folders are functional.
notes:
GHOST_SystemPathsCocoa.mm has two functions : one to get all required attributes/ resourcekeys using NSURLResourceKey methods; other resolves file path and copies it in the provided buffer. All other ghost files are wrappers around it.

