Core/Instances: Delete InstanceSaveMgr and replace most of its uses with new InstanceLockMgr

Port From (https://github.com/TrinityCore/TrinityCore/commit/9b924522d0549dd67b10e2cbdfc20297dd21e182)

Source/Game/Globals/ObjectManager.cs

@@ -12061,4 +12061,10 @@ namespace Game
             }
         }
     }
+
+    public class InstanceTemplate
+    {
+        public uint Parent;
+        public uint ScriptId;
+    }
 }