Core/Objects: Unify Searcher classes into one common implementation

Port From (https://github.com/TrinityCore/TrinityCore/commit/261eb201bf107cef441d9b075e8f23bf0edfbaf0)
Port From (https://github.com/TrinityCore/TrinityCore/commit/526b16fea41fb69a302fdebe8a727e175949f04b)
Port From (https://github.com/TrinityCore/TrinityCore/commit/8b7dce6521323e788ebf28297ec941a6f9bf876f)
Port From (https://github.com/TrinityCore/TrinityCore/commit/5334467f493eb16141f4ad0bce956bc3e19244a0)
Port From (https://github.com/TrinityCore/TrinityCore/commit/1e7725c15b149baaf96731231239769e482ec2ed)
Port From (https://github.com/TrinityCore/TrinityCore/commit/21712f475383f6f3fae107706f5de5195f75b760)

Source/Game/World/WorldManager.cs

@@ -2728,15 +2728,17 @@ namespace Game
         uint i_textId;
         object[] i_args;
 
-        public class MultiplePacketSender : IDoWork<Player>
+        public class MultiplePacketSender
         {
+            public List<ServerPacket> Packets = new();
+
             public void Invoke(Player receiver)
             {
                 foreach (var packet in Packets)
                     receiver.SendPacket(packet);
             }
 
-            public List<ServerPacket> Packets = new();
+            public static implicit operator IDoWork<Player>(MultiplePacketSender obj) => obj.Invoke;
         }
     }