Core/AI: Add a new LeavingWorld AI hook

(cherry picked from commit c0a7274ff1)

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

@@ -284,6 +284,9 @@ class TC_GAME_API UnitAI
         // Called when the unit leaves combat
         virtual void JustExitedCombat() { }
 
+        // Called when the unit is about to be removed from the world (despawn, grid unload, corpse disappearing, player logging out etc.)
+        virtual void LeavingWorld() { }
+
         // Called at any Damage to any victim (before damage apply)
         virtual void DamageDealt(Unit* /*victim*/, uint32& /*damage*/, DamageEffectType /*damageType*/) { }
 

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

@@ -9064,6 +9064,9 @@ void Unit::RemoveFromWorld()
     if (IsInWorld())
     {
         m_duringRemoveFromWorld = true;
+        if (IsAIEnabled)
+            GetAI()->LeavingWorld();
+
         if (IsVehicle())
             RemoveVehicleKit(true);