Enhancement: copyFiles buildPhase using Products

First thing first, let me show you concept:

Note that this is just a concept and is not a valid syntax

targets:
    Sample Application:
        type: application
        platform: macOS
        sources:
              target: Helper
              optional: true
              buildPhase:
                  copyFiles:
                      destination: wrapper
                      subpath: $(CONTENTS_FOLDER_PATH)/Library/LoginItems
    Helper:
        type: application
        platform: macOS

• Here I'm creating Sample Application which is the main application target, and the helper application Helper. Helper application will be used to toggle Launch on Login feature which is seen in many applications. To make it work, a helper application must be included in the main app bundle, in this case it's:
  Sample Application.app/Contents/Library/LoginItems/Helper.app.
  • This is the latest and valid way to achieve the feature as of today.
  • Reference: https://developer.apple.com/library/archive/documentation/MacOSX/Conceptual/BPSystemStartup/Chapters/CreatingLoginItems.html

Back to xcodegen, if I'm correct, this is not possible as of v2.18.0 (Please correct me if I'm missing something).
The above is just an example to explain the usefulness if it's possible. And this is not specific to the LoginItem thing, there may be other cases that can use this approach, I guess.
Thus, "copyFiles buildPhase using Products". (I'm not sure if sources is the suitable location to put them, this is just a concept)

What do you think?

No files, tests, or entry points are named. Start by reviewing how XcodeGen v2.18.0 represents sources, Products, and copyFiles build phases, then compare that model with the YAML concept and define coverage for copying a Helper product into the specified wrapper subpath. Done means the supported syntax and its generated Xcode project behavior are documented and tested.