lib/modules: Evaluate single defs for readOnly error
lib/modules: Evaluate single defs for readOnly error

If multiple definitions are passed, this evaluates them all as if they
were the only one, for a better error message. In particular this won't
show module-internal properties like `_type = "override"` and co.

NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs