Core/AI: Add a new LeavingWorld AI hook

src/server/game/Entities/Unit/Unit.cpp

@@ -10038,6 +10038,9 @@ void Unit::RemoveFromWorld()
     if (IsInWorld())
     {
         m_duringRemoveFromWorld = true;
+        if (IsAIEnabled)
+            GetAI()->LeavingWorld();
+
         if (IsVehicle())
             RemoveVehicleKit();