Core/Items: Addes support for calculating item level & cleanup iterating over items.

Based on https://github.com/TrinityCore/TrinityCore/pull/26276

Source/Game/Handlers/AzeriteHandler.cs

@@ -65,7 +65,7 @@ namespace Game
             ActivateEssenceFailed activateEssenceResult = new();
             activateEssenceResult.AzeriteEssenceID = azeriteEssenceActivateEssence.AzeriteEssenceID;
 
-            Item item = _player.GetItemByEntry(PlayerConst.ItemIdHeartOfAzeroth, ItemSearchLocation.InEquipment);
+            Item item = _player.GetItemByEntry(PlayerConst.ItemIdHeartOfAzeroth, ItemSearchLocation.Equipment);
             if (item == null)
             {
                 activateEssenceResult.Reason = AzeriteEssenceActivateResult.NotEquipped;

Source/Game/Handlers/CharacterHandler.cs

@@ -1024,6 +1024,9 @@ namespace Game
             if (!pCurrChar.IsStandState() && !pCurrChar.HasUnitState(UnitState.Stunned))
                 pCurrChar.SetStandState(UnitStandStateType.Stand);
 
+            pCurrChar.UpdateAverageItemLevelTotal();
+            pCurrChar.UpdateAverageItemLevelEquipped();
+
             m_playerLoading.Clear();
 
             Global.ScriptMgr.OnPlayerLogin(pCurrChar);