Properly stop attacking after player leaves ffa area (like Gurubashi Arena)

Port From (https://github.com/TrinityCore/TrinityCore/commit/4380fe2751869e7a011d51ee9449e8723b00067f)

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

@@ -110,9 +110,14 @@ namespace Game.Entities
             m_areaUpdateId = newArea;
 
             AreaTableRecord area = CliDB.AreaTableStorage.LookupByKey(newArea);
+            bool oldFFAPvPArea = pvpInfo.IsInFFAPvPArea;
             pvpInfo.IsInFFAPvPArea = area != null && area.Flags[0].HasAnyFlag(AreaFlags.Arena);
             UpdatePvPState(true);
 
+            // check if we were in ffa arena and we left
+            if (oldFFAPvPArea && !pvpInfo.IsInFFAPvPArea)
+                ValidateAttackersAndOwnTarget();
+
             PhasingHandler.OnAreaChange(this);
             UpdateAreaDependentAuras(newArea);
 

Source/Game/Entities/Unit/Unit.Combat.cs

@@ -225,6 +225,24 @@ namespace Game.Entities
             }
         }
 
+        public void ValidateAttackersAndOwnTarget()
+        {
+            // iterate attackers
+            List<Unit> toRemove = new List<Unit>();
+            foreach (Unit attacker in getAttackers())
+                if (!attacker.IsValidAttackTarget(this))
+                    toRemove.Add(attacker);
+
+            foreach (Unit attacker in toRemove)
+                attacker.AttackStop();
+
+            // remove our own victim
+            Unit victim = GetVictim();
+            if (victim != null)
+                if (!IsValidAttackTarget(victim))
+                    AttackStop();
+        }
+
         public void CombatStop(bool includingCast = false)
         {
             if (includingCast && IsNonMeleeSpellCast(false))