modules: move nixpkgs module to top-level modules

Make `pkgs` available to files submodules by passing _all_ module args
through. We already did this for `specialArgs`.

modules/misc/default.nix

@@ -3,7 +3,6 @@
     ./assertions.nix
     ./context.nix
     ./meta.nix
-    ./nixpkgs.nix
     ./nixvim-info.nix
   ];
 }

modules/top-level/default.nix

@@ -7,6 +7,7 @@
   imports = [
     ../.
     ./files
+    ./nixpkgs.nix
     ./output.nix
     ./readonly-renames.nix
     ./test.nix

modules/top-level/files/default.nix

@@ -15,6 +15,15 @@ let
     modules = lib.optionals (!config.isDocs) [
       ../../.
       ./submodule.nix
+      # Pass module args through to the submodule (except `name`)
+      # Wrap each arg with the correct priority
+      {
+        _module.args = lib.pipe options._module.args [
+          lib.modules.mergeAttrDefinitionsWithPrio
+          (lib.flip builtins.removeAttrs [ "name" ])
+          (lib.mapAttrs (_: { highestPrio, value }: lib.mkOverride highestPrio value))
+        ];
+      }
     ];
     description = "Nixvim configuration";
   };