Consistent relative paths to expression file

[willbush]

🚀 Catalyst

#2 (comment)

📃 Description

PR has changes needed to output error messages with paths relative to expression
file instead of nixpkgs root.

• tests: move all-packages.nix to pkgs/top-level

  In this commit I move all the tests/*/all-packages.nix to tests/*/pkgs/top-level/all-packages.nix without changing any code (breaking a lot of tests).

  The reason for this commit is to make it more obvious in the expected files results where changes where needed to get ./pkgs/by-name to become ./../by-name

• Fix relative paths in all-packages.nix files and expected outputs

  This commit just gets tests passing again before I start modifying other code.

• Update errors paths to be relative to the expression file

  Most changes are here to use relative paths to expression file in all cases.

[willbush]

Annoying. I thought moving files in one commit without modifying meant git would detect it as a move. Guess I should have used git mv explicitly. Should I bother trying to fix it?

[infinisil]

If you look at the diff commit-by-commit it works, so that seems fine to me :)

[infinisil]

This looks good to me, thanks a lot!