refactor: rename to $__toObjectShallow() based on code review comments

Author: vkarpov15

lib/document.js

@@ -3866,7 +3866,7 @@ Document.prototype.$toObject = function(options, json) {
   if (hasOnlyPrimitiveValues && !options.flattenObjectIds) {
     // Fast path: if we don't have any nested objects or arrays, we only need a
     // shallow clone.
-    ret = this.$__toObjectInternal();
+    ret = this.$__toObjectShallow();
   } else {
     ret = clone(this._doc, options) || {};
   }
@@ -3931,7 +3931,7 @@ Document.prototype.$toObject = function(options, json) {
  * Internal shallow clone alternative to `$toObject()`: much faster, no options processing
  */
 
-Document.prototype.$__toObjectInternal = function $__toObjectInternal() {
+Document.prototype.$__toObjectShallow = function $__toObjectShallow() {
   const ret = {};
   if (this._doc != null) {
     for (const key of Object.keys(this._doc)) {

lib/model.js

@@ -2954,7 +2954,7 @@ Model.$__insertMany = function(arr, options, callback) {
         doc.initializeTimestamps();
       }
       if (doc.$__hasOnlyPrimitiveValues()) {
-        return doc.$__toObjectInternal();
+        return doc.$__toObjectShallow();
       }
       return doc.toObject(internalToObjectOptions);
     });