Need to handle macOS alias files

These are not the same as symbolic links, and won't get resolved automatically.

Problem:
- create an alias of (say) a .designspace file
- try to open the alias with Fontra Pak
- Fontra will try to interpret the raw alias data as .designspace, which obviously fails

The issue names no files or tests. Start by locating the file-opening or path-resolution entry point that receives a macOS alias, then compare its behavior with symbolic links; done means an alias to a .designspace file is resolved before Fontra parses it.

Written by the indexing model from the issue text.