fix: Nested objects are encoded incorrectly for MongoDB (#8209)

BREAKING CHANGE: Nested objects are now properly stored in the database using JSON serialization; previously, due to a bug only top-level objects were serialized, but nested objects were saved as raw JSON; for example, a nested `Date` object was saved as a JSON object like `{ "__type": "Date", "iso": "2020-01-01T00:00:00.000Z" }` instead of its serialized representation `2020-01-01T00:00:00.000Z` (#8209)

src/Adapters/Storage/Mongo/MongoTransform.js

@@ -1014,6 +1014,9 @@ function mapValues(object, iterator) {
   const result = {};
   Object.keys(object).forEach(key => {
     result[key] = iterator(object[key]);
+    if (result[key] && JSON.stringify(result[key]).includes(`"__type"`)) {
+      result[key] = mapValues(object[key], iterator);
+    }
   });
   return result;
 }