[dart-dio] fix JsonObject missing on a generated code OpenAPITools#16585 (OpenAPITools#19130)

* fix: issue 16261. JsonObject is missing on a generated code

* update samples

---------

Co-authored-by: toriumi0118 <[email protected]>

Author: wing328

modules/openapi-generator/src/main/resources/dart/libraries/dio/serialization/built_value/api/imports.mustache

@@ -1 +1,2 @@
+import 'package:built_value/json_object.dart';
 import 'package:built_value/serializer.dart';

samples/openapi3/client/petstore/dart-dio/oneof/lib/src/api/default_api.dart

@@ -4,6 +4,7 @@
 
 import 'dart:async';
 
+import 'package:built_value/json_object.dart';
 import 'package:built_value/serializer.dart';
 import 'package:dio/dio.dart';
 

samples/openapi3/client/petstore/dart-dio/oneof_polymorphism_and_inheritance/lib/src/api/bar_api.dart

@@ -4,6 +4,7 @@
 
 import 'dart:async';
 
+import 'package:built_value/json_object.dart';
 import 'package:built_value/serializer.dart';
 import 'package:dio/dio.dart';
 

samples/openapi3/client/petstore/dart-dio/oneof_polymorphism_and_inheritance/lib/src/api/foo_api.dart

@@ -4,6 +4,7 @@
 
 import 'dart:async';
 
+import 'package:built_value/json_object.dart';
 import 'package:built_value/serializer.dart';
 import 'package:dio/dio.dart';
 

samples/openapi3/client/petstore/dart-dio/oneof_primitive/lib/src/api/default_api.dart

@@ -4,6 +4,7 @@
 
 import 'dart:async';
 
+import 'package:built_value/json_object.dart';
 import 'package:built_value/serializer.dart';
 import 'package:dio/dio.dart';
 

samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/src/api/another_fake_api.dart

@@ -4,6 +4,7 @@
 
 import 'dart:async';
 
+import 'package:built_value/json_object.dart';
 import 'package:built_value/serializer.dart';
 import 'package:dio/dio.dart';
 

samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/src/api/default_api.dart

@@ -4,6 +4,7 @@
 
 import 'dart:async';
 
+import 'package:built_value/json_object.dart';
 import 'package:built_value/serializer.dart';
 import 'package:dio/dio.dart';
 

samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/src/api/fake_api.dart

@@ -4,6 +4,7 @@
 
 import 'dart:async';
 
+import 'package:built_value/json_object.dart';
 import 'package:built_value/serializer.dart';
 import 'package:dio/dio.dart';
 

samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/src/api/fake_classname_tags123_api.dart

@@ -4,6 +4,7 @@
 
 import 'dart:async';
 
+import 'package:built_value/json_object.dart';
 import 'package:built_value/serializer.dart';
 import 'package:dio/dio.dart';
 

samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/src/api/pet_api.dart

@@ -4,6 +4,7 @@
 
 import 'dart:async';
 
+import 'package:built_value/json_object.dart';
 import 'package:built_value/serializer.dart';
 import 'package:dio/dio.dart';
 

samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/src/api/store_api.dart

@@ -4,6 +4,7 @@
 
 import 'dart:async';
 
+import 'package:built_value/json_object.dart';
 import 'package:built_value/serializer.dart';
 import 'package:dio/dio.dart';
 

samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake/lib/src/api/user_api.dart

@@ -4,6 +4,7 @@
 
 import 'dart:async';
 
+import 'package:built_value/json_object.dart';
 import 'package:built_value/serializer.dart';
 import 'package:dio/dio.dart';