This fixes an error in nixpkgs-review when it tries to pass this to
buildEnv:
error: The store path [...]project-references-test is a file and can't
be merged into an environment using pkgs.buildEnv! at [...]-builder.pl
line 122.
This change refactors internal hooks used by buildDotnetModule to
support derivations with structured attributes. Note that this changes
variable names that the internal hooks expect.
