(darwin) fix app linking

[lylythechosenone]

Description

Link the Contents subfolder of each individual app rather than a folder containing all apps, thereby enabling the apps to appear in Spotlight and Launchpad.

I'm not a nix master, so I fully expect at least some of this to be the wrong way to do it. Please correct me if it is.

Checklist

• Change is backwards compatible. — all options are the same. The file structure is the same, but some files have become links, and some links have become files.

• Code formatted with nix fmt or
  nix-shell -p treefmt nixfmt-rfc-style keep-sorted --run treefmt.

• Code tested through nix-shell --pure tests -A run.all
  or nix build --reference-lock-file flake.lock ./tests#test-all using Flakes. — tested to work for its intended purpose. I don't currently have the capacity to run all tests.

• Test cases updated/added. See example.

• Commit messages are formatted like — I got close; I'm not sure how to change the message from gitweb, sadly.

  {component}: {description}
  
  {long description}
  

  See CONTRIBUTING for more information and recent commit messages for examples.

• If this PR adds a new module

  • Added myself as module maintainer. See example.

Maintainer CC

[lylythechosenone]

Actually, I'm rescinding this for now, as it seems to have broken after a reboot/update (not sure why). I will investigate.