Modify stub handling to allow for console and GUI stubs

[freakboy3742]

Modifies the stub handling so that there are 2 binary stubs - one for GUI, and one for console.

The post-processing step moves the correct binary to the Stub name (rather than <Formal Name>), and deletes the unneeded binaries. The Stub name is used as part of a fix for beeware/briefcase#1729.

This PR cannot be completed until beeware/briefcase-macOS-Xcode-template#41 is completed, as the new app binaries need to be generated using the new Xcode template.

Refs beeware/briefcase#1781

Briefcase-Repo: https://github.com/freakboy3742/briefcase.git
Briefcase-Ref: cmdline-app

PR Checklist:

• All new features have been tested
• All new features have been documented
• I have read the CONTRIBUTING.md file
• I will abide by the code of conduct

[freakboy3742]

I've now pushed updated binaries for the console and GUI stubs; this should be ready for final testing.