modules/output: Allow to specify text to add as extra files (#343)

To enable some features (like adding tree-sitter queries) we need to add
files to specific directories in the runtime path (queries/lang/file.scm
for tree-sitter queries for example).

This commit adds support for specifying such files. You must be careful
to not have any collisions between `files` and `extraFiles`.

wrappers/_shared.nix

@@ -26,12 +26,24 @@ in {
   configFiles = let
     cfg = config.programs.nixvim;
   in
-    lib.mapAttrs'
     (
-      _: file:
-        lib.nameValuePair
-        "nvim/${file.path}"
-        {text = file.content;}
+      lib.mapAttrs'
+      (
+        _: file:
+          lib.nameValuePair
+          "nvim/${file.path}"
+          {text = file.content;}
+      )
+      cfg.files
     )
-    cfg.files;
+    // (
+      lib.mapAttrs'
+      (
+        path: content:
+          lib.nameValuePair
+          "nvim/${path}"
+          {text = content;}
+      )
+      cfg.extraFiles
+    );
 }