perf(document): add fast path for applying non-nested virtuals to JSON

Re: #14394

Author: vkarpov15

lib/document.js

@@ -4130,6 +4130,14 @@ function applyVirtuals(self, json, options, toObjectOptions) {
       }
       assignPath = path.substring(options.path.length + 1);
     }
+    if (assignPath.indexOf('.') === -1 && assignPath === path) {
+      v = clone(self.get(path, options ? { ...options, noDottedPath: true } : { noDottedPath: true }));
+      if (v === void 0) {
+        continue;
+      }
+      json[assignPath] = v;
+      continue;
+    }
     const parts = assignPath.split('.');
     v = clone(self.get(path), options);
     if (v === void 0) {