Core/Unit: make neutral guards attack players involved in PvP

Port From (https://github.com/TrinityCore/TrinityCore/commit/a58dcd1d9cf5f943342d00628601170d6023ae25)

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

@@ -3183,6 +3183,9 @@ namespace Game.Entities
                     Player player = playerAffectingAttacker ? playerAffectingAttacker : playerAffectingTarget;
                     Unit creature = playerAffectingAttacker ? target : this;
 
+                    if (creature.IsContestedGuard() && player.HasPlayerFlag(PlayerFlags.ContestedPVP))
+                        return true;
+
                     var factionTemplate = creature.GetFactionTemplateEntry();
                     if (factionTemplate != null)
                     {

Source/Game/Entities/Unit/Unit.cs

@@ -799,6 +799,15 @@ namespace Game.Entities
         public bool IsCritter() { return GetCreatureType() == CreatureType.Critter; }
         public bool IsInFlight() { return HasUnitState(UnitState.InFlight); }
 
+        public bool IsContestedGuard()
+        {
+            var entry = GetFactionTemplateEntry();
+            if (entry != null)
+                return entry.IsContestedGuardFaction();
+
+            return false;
+        }
+        
         public void SetHoverHeight(float hoverHeight) { SetUpdateFieldValue(m_values.ModifyValue(m_unitData).ModifyValue(m_unitData.HoverHeight), hoverHeight); }
 
         public override float GetCollisionHeight()