Core/Objects: Refactor private object checks into separate function

Port From (https://github.com/TrinityCore/TrinityCore/commit/f21270b987211041b95d6befa7192d313692920d)

Source/Game/Combat/ThreatManager.cs

@@ -87,8 +87,8 @@ namespace Game.Combat
             uint redirectThreadPct = victim.GetRedirectThreatPercent();
             Unit redirectTarget = victim.GetRedirectThreatTarget();
 
-            // If victim is personnal spawn, redirect all aggro to summoner
-            if (victim.IsPrivateObject() && GetOwner().IsPrivateObject() && GetOwner().CanSeeOrDetect(victim))
+            // If victim is personal spawn, redirect all aggro to summoner
+            if (victim.IsPrivateObject() && (!GetOwner().IsPrivateObject() || !GetOwner().CheckPrivateObjectOwnerVisibility(victim)))
             {
                 redirectThreadPct = 100;
                 redirectTarget = Global.ObjAccessor.GetUnit(GetOwner(), victim.GetPrivateObjectOwner());

Source/Game/Entities/Object/WorldObject.cs

@@ -1100,20 +1100,36 @@ namespace Game.Entities
             return 0.0f;
         }
 
+        public bool CheckPrivateObjectOwnerVisibility(WorldObject seer)
+        {
+            if (!IsPrivateObject())
+                return true;
+
+            // Owner of this private object
+            if (_privateObjectOwner == seer.GetGUID())
+                return true;
+
+            // Another private object of the same owner
+            if (_privateObjectOwner == seer.GetPrivateObjectOwner())
+                return true;
+
+            return false;
+        }
+        
         public bool CanSeeOrDetect(WorldObject obj, bool ignoreStealth = false, bool distanceCheck = false, bool checkAlert = false)
         {
             if (this == obj)
                 return true;
 
-            if (!obj.GetPrivateObjectOwner().IsEmpty())
-                return GetGUID() == obj.GetPrivateObjectOwner() || GetPrivateObjectOwner() == obj.GetPrivateObjectOwner();
-
             if (obj.IsNeverVisibleFor(this) || CanNeverSee(obj))
                 return false;
 
             if (obj.IsAlwaysVisibleFor(this) || CanAlwaysSee(obj))
                 return true;
 
+            if (!obj.CheckPrivateObjectOwnerVisibility(this))
+                return false;
+
             bool corpseVisibility = false;
             if (distanceCheck)
             {

Source/Game/Maps/GridNotifiers.cs

@@ -2300,7 +2300,7 @@ namespace Game.Maps
 
         public bool Invoke(Creature u)
         {
-            if (u.GetDeathState() != DeathState.Dead && u.GetEntry() == i_entry && u.IsAlive() == i_alive && i_obj.IsWithinDistInMap(u, i_range) && u.CanSeeOrDetect(i_obj))
+            if (u.GetDeathState() != DeathState.Dead && u.GetEntry() == i_entry && u.IsAlive() == i_alive && i_obj.IsWithinDistInMap(u, i_range) && u.CheckPrivateObjectOwnerVisibility(i_obj))
             {
                 i_range = i_obj.GetDistance(u);         // use found unit range as new range limit for next check
                 return true;