[cpp-ue4] Added UE4.26 support, (#8964)

* [cpp-ue4] Fixed enum values not being quoted. I'm not sure when this started breaking.

* [cpp-ue4] UE 4.26 Compatibility: Replaced TSharedRef<IHttpRequest by FHttpRequestRef for better portability

* [cpp-ue4] Improved DateTime parsing

* [cpp-ue4] Made HttpFileInput constructors explicit

* [cpp-ue4] Added the possibility to retry requests easily with AsyncRetry method on the response and SetAutoRetryCount on the request

WIP auto retry

[cpp-ue4] Adds support for instant retry

* [cpp-ue4] Using TaskGraph instead of TaskGraphMainThread for async retries

* update samples

* remove trailing spaces

Co-authored-by: Jean-Noel Gourdol <jngourdol@stormancer.com>
Co-authored-by: William Cheng <wing328hk@gmail.com>

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

@@ -12,6 +12,8 @@
 
 #include "OpenAPIBaseModel.h"
 
+#include "Async/Async.h"
+
 namespace OpenAPI 
 {
 
@@ -25,4 +27,13 @@ void Response::SetHttpResponseCode(EHttpResponseCodes::Type InHttpResponseCode)
     }
 }
 
+void Response::AsyncRetry() const
+{
+    // Unfortunately, it is currently usafe to call ProcessRequest() directly here.
+    // This is because the HttpManager will remove all references to this HttpRequest in FHttpManager::Tick including the new request we just added, instead of removing just one. 
+    // This will lead to the request's destruction and eventually a crash.
+    // The only solution is therefore to ensure we are taking an extra reference to the request, and that the request is added after the queue is flushed.
+    Async(EAsyncExecution::TaskGraph, [AddRef = FHttpRequestPtr(GetHttpRequest())](){ AddRef->ProcessRequest(); });
+}
+
 }