Refactor/simplify Mac binary packaging script

The mac packaging script (//mkdist/mainline/installers/mac-binary/package/mkpackage) has been around for a long time without any refactoring. Given that there have been significant changes to packaging and licensing over the last two years, the script should be reviewed with the goal of making it simpler and easier to maintain. For example, differences between carbon and cocoa packages should be clear, as carbon packages will be dropped at some future time.

During the process of refactoring, transitioning from shell script to Perl is permissible, and probably desirable.