[C++][Ue4] various bus fixes (#6539)

* Fixed compilation on linux and UE4.23

* Added string and enum type definition support

* Better handling or variable names, should avoid conflicts with reserved keywords or empty variable names in edge cases

* Updated samples

samples/client/petstore/cpp-ue4/Private/OpenAPIHelpers.cpp

@@ -17,6 +17,7 @@
 #include "Interfaces/IHttpRequest.h"
 #include "PlatformHttp.h"
 #include "Misc/FileHelper.h"
+#include "Misc/Paths.h"
 
 namespace OpenAPI 
 {