Unpack/Repack Pkg Tooling and Tests

[ellahathaway]

Related to #14438

This PR introduces a tool that unpacks and repacks .pkg files and nested .app bundles. It also includes test cases and test data for the tool.

The MacOS PKG tool includes the following components:

• Program.cs: Driver for unpacking and packing .pkg files and .app bundles.
• Package.cs: Class representing a .pkg, responsible for unpacking and repacking .pkg installer packages and component packages.
• AppBundle.cs: Class representing an .app bundle, which unpacks and repacks .app directories into .zip files. This is necessary for Enable signing and notarization of .pkg files using SignTool #14435
• Utilities.cs: Class that contains helper functions.
• ExecuteHelper.cs: Class that runs processes.

[ellahathaway]

I'm going to update the tests to include checks against the checksums. When I did this check locally, the checksums were different. I verified that it's the Bom files that are different, so I'm currently working to identify why that is.

In the meantime, I think that the PR is still worth reviewing so I'm going to leave this undrafted.

[ellahathaway]

I'm going to update the tests to include checks against the checksums. When I did this check locally, the checksums were different. I verified that it's the Bom files that are different, so I'm currently working to identify why that is.

In the meantime, I think that the PR is still worth reviewing so I'm going to leave this undrafted.

Filed #15219 to investigate this at a later time.

[mmitche]

Because this can only be run on Mac, this should not need NetFrameworkToolCurrent, correct?