Core/Loot: Prevent looting bosses by players that have already completed that encounter

Port From (https://github.com/TrinityCore/TrinityCore/commit/9ce47e6809eecc891904e272b368596fdc55e6a4)

Source/Game/Entities/Player/Player.Items.cs

@@ -5973,7 +5973,7 @@ namespace Game.Entities
                 return;
             }
 
-            if (!item.AllowedForPlayer(this))
+            if (!item.HasAllowedLooter(GetGUID()))
             {
                 SendLootReleaseAll();
                 return;

Source/Game/Entities/Player/Player.Map.cs

@@ -558,6 +558,19 @@ namespace Game.Entities
             SendPacket(transferAborted);
         }
 
+        public bool IsLockedToDungeonEncounter(uint dungeonEncounterId)
+        {
+            DungeonEncounterRecord dungeonEncounter = CliDB.DungeonEncounterStorage.LookupByKey(dungeonEncounterId);
+            if (dungeonEncounter == null)
+                return false;
+
+            InstanceLock instanceLock = Global.InstanceLockMgr.FindActiveInstanceLock(GetGUID(), new MapDb2Entries(GetMap().GetEntry(), GetMap().GetMapDifficulty()));
+            if (instanceLock == null)
+                return false;
+
+            return (instanceLock.GetData().CompletedEncountersMask & (1u << dungeonEncounter.Bit)) != 0;
+        }
+        
         public override void ProcessTerrainStatusUpdate(ZLiquidStatus oldLiquidStatus, LiquidData newLiquidData)
         {
             // process liquid auras using generic unit code

Source/Game/Entities/Player/Player.cs

@@ -3130,7 +3130,8 @@ namespace Game.Entities
             Loot loot = creature.GetLootForPlayer(this);
             if (loot == null || loot.IsLooted()) // nothing to loot or everything looted.
                 return false;
-            if (!loot.HasItemForAll() && !loot.HasItemFor(this)) // no loot in creature for this player
+
+            if (!loot.HasAllowedLooter(GetGUID()) || (!loot.HasItemForAll() && !loot.HasItemFor(this))) // no loot in creature for this player
                 return false;
 
             if (loot.loot_type == LootType.Skinning)