Provide rvalue cast operator for ResultValue

Allows objects returned as ResultValue (instead of
ResultValueType::type) to be moved without requiring
additional casting or explicit use of ResultValue::value.

Resolves #589

VulkanHppGenerator.cpp

@@ -7859,6 +7859,11 @@ namespace std
     {
       return value;
     }
+
+    operator T&& () && VULKAN_HPP_NOEXCEPT
+    {
+      return std::move( value );
+    }
 #endif
   };