feat(Core/AI): add the UnitAI::OnDespawn hook (#27285)

Co-authored-by: Treeston <treeston.mmoc@gmail.com>

src/server/game/AI/CoreAI/UnitAI.h

@@ -355,6 +355,11 @@ public:
      */
     virtual void JustExitedCombat() { }
 
+    /**
+     * @brief Called when the unit is about to be removed from the world (despawn, grid unload, corpse disappearing, player logging out etc.)
+     */
+    virtual void OnDespawn() { }
+
     /**
      * @brief Called when evade timer expires (target unreachable for too long)
      */

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

@@ -12561,6 +12561,9 @@ void Unit::RemoveFromWorld()
     if (IsInWorld())
     {
         m_duringRemoveFromWorld = true;
+        if (IsAIEnabled)
+            GetAI()->OnDespawn();
+
         if (IsVehicle())
             RemoveVehicleKit();