Core/Maps: Check group that owns instance (first group to enter a given instance id owns it)

Port From (https://github.com/TrinityCore/TrinityCore/commit/a131542855d23022714a97640be1c8d68a741c31)

Source/Game/Maps/Map.cs

@@ -4914,7 +4914,7 @@ namespace Game.Maps
             if (i_instanceLock != null)
             {
                 MapDb2Entries entries = new(GetEntry(), GetMapDifficulty());
-                if (entries.IsInstanceIdBound() || IsRaid() || entries.MapDifficulty.IsRestoringDungeonState() || !i_owningGroupRef.isValid())
+                if (entries.IsInstanceIdBound() || IsRaid() || entries.MapDifficulty.IsRestoringDungeonState() || !i_owningGroupRef.IsValid())
                 {
                     InstanceLockData lockData = i_instanceLock.GetInstanceInitializationData();
                     i_data.SetCompletedEncountersMask(lockData.CompletedEncountersMask);
@@ -4931,6 +4931,14 @@ namespace Game.Maps
                 i_data.Create();
         }
 
+        public Group GetOwningGroup() { return i_owningGroupRef.GetTarget(); }
+        
+        public void TrySetOwningGroup(Group group)
+        {
+            if (!i_owningGroupRef.IsValid())
+                i_owningGroupRef.Link(group, this);
+        }
+
         public bool Reset(InstanceResetMethod method)
         {
             // note: since the map may not be loaded when the instance needs to be reset
@@ -5149,6 +5157,7 @@ namespace Game.Maps
         uint i_script_id;
         InstanceScenario i_scenario;
         InstanceLock i_instanceLock;
+        GroupInstanceReference i_owningGroupRef = new();
         bool m_resetAfterUnload;
         bool m_unloadWhenEmpty;
     }