kern: devirtualize KAutoObject::DynamicCast<>()

This is an optimization that saves the most common type of virtual call in the kernel (DynamicCast)
by storing class token as a member, rather than getting it via virtual call every time.

This does not currently cost any memory space on 64-bit targets, due to pre-existing padding space.

This optimization can be turned off via a compile-time flag for accuracy.

libraries/libmesosphere/source/kern_k_auto_object.cpp

@@ -19,6 +19,11 @@ namespace ams::kern {
 
     KAutoObject *KAutoObject::Create(KAutoObject *obj) {
         obj->m_ref_count = 1;
+
+        #if defined(MESOSPHERE_ENABLE_DEVIRTUALIZED_DYNAMIC_CAST)
+        obj->m_class_token = obj->GetTypeObj().GetClassToken();
+        #endif
+
         return obj;
     }