nix build --dry-run
Don’t try and assume that we know the output paths when we’ve just built with `--dry-run`. Instead make `--dry-run` follow a different code path that won’t assume the knowledge of the output paths at all. Fix #6275
Replace `DerivedPathWithHints` by a new `BuiltPath` type that serves as a proof that the corresponding path has been built.
Just a renaming for now