Support language N4JS (#15089)

* n4js initial commit

* incorporate feedback from user

* add tests

* fix media type in case of DELETE method

* fix media type

* some minor fixes

* options fix for booleans

* small fixes

* generated files by ./bin/utils/ensure-up-to-date

* remove String::toLowerCase due to de.thetaphi:forbiddenapis

* adjust test expectation

* fix test expectations

* fix test expectation

* add note to section 'Languages/Generators'

* remove file according to review

samples/client/petstore/n4js/model/User.n4jsd

@@ -0,0 +1,30 @@
+/*
+ * OpenAPI Petstore
+ * This is a sample server Petstore server. For this sample, you can use the api key `special-key` to test the authorization filters.
+ *
+ * The version of the OpenAPI document: 1.0.0
+ * 
+ *
+ * NOTE: This class is auto generated by OpenAPI Generator (https://openapi-generator.tech).
+ * https://openapi-generator.tech
+ * Do not edit the class manually.
+ */
+
+
+/**
+ * A User who is purchasing from the pet store
+ */
+export external public interface ~User {
+    public id?: int;
+    public username?: string;
+    public firstName?: string;
+    public lastName?: string;
+    public email?: string;
+    public password?: string;
+    public phone?: string;
+
+    /**
+     * User Status
+     */
+    public userStatus?: int;
+}