LoadEngineDLL.h: include only minimal required Windows headers

This avoids the need to use WinHPostface.h in public headers
and does not leak Windows defines

Author: TheMostDiligent

Graphics/GraphicsEngine/interface/LoadEngineDll.h

@@ -39,9 +39,8 @@
 #    include "../../../Common/interface/StringTools.hpp"
 #endif
 
-#include "../../../Platforms/Win32/interface/WinHPreface.h"
-#include <Windows.h>
-#include "../../../Platforms/Win32/interface/WinHPostface.h"
+#include <libloaderapi.h>
+#include <debugapi.h>
 
 DILIGENT_BEGIN_NAMESPACE(Diligent)