Add C++ UE4 client generator (#6399)

* Added new language: UE4 C++ client

* rename generator

* add copyright

* update doc

* fix with Locale.ROOT

* add new file

* minor improvements

* remove postProcessModels

Co-authored-by: Samuel Kahn <samuel@kahncode.com>

samples/client/petstore/cpp-ue4/OpenAPI.Build.cs

@@ -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.
+ *
+ * OpenAPI spec version: 1.0.0
+ * 
+ *
+ * NOTE: This class is auto generated by OpenAPI Generator
+ * https://github.com/OpenAPITools/openapi-generator
+ * Do not edit the class manually.
+ */
+
+using System;
+using System.IO;
+using UnrealBuildTool;
+
+public class OpenAPI : ModuleRules
+{
+    public OpenAPI(ReadOnlyTargetRules Target) : base(Target)
+    {
+        PublicDependencyModuleNames.AddRange(
+            new string[]
+            {
+                "Core",
+                "Http",
+                "Json",
+            }
+        );
+    }
+}