lib/modules: Internally collect all unmatched definitions
lib/modules: Internally collect all unmatched definitions

This fundamentally changes how the module evaluation internally
handles definitions without an associated option.

Previously the values of these definitions were discarded and only
the names were propagated. This was fine because that's all that's
needed for optionally checking whether all definitions have an
associated option with _module.check.

However with the upcoming change of supporting freeform modules,
we *do* need the values of these.

With this change, the module evaluation cleanly separates definitions
that match an option, and ones that do not.

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