Add handler for unknown Discord dispatch events (#3088)

Author: Spider570

src/Discord.Net.WebSocket/BaseSocketClient.Events.cs

@@ -1,5 +1,5 @@
 using Discord.Rest;
-
+using Newtonsoft.Json.Linq;
 using System;
 using System.Collections.Generic;
 using System.Threading.Tasks;
@@ -1069,5 +1069,20 @@ public event Func<Cacheable<SocketSubscription, ulong>, Task> SubscriptionDelete
         internal readonly AsyncEvent<Func<Cacheable<SocketSubscription, ulong>, Task>> _subscriptionDeleted = new();
 
         #endregion
+
+        #region Others
+
+        /// <summary>
+        ///     Fired when a dispatch event is received from Discord that does not match any known event type.
+        /// </summary>
+        public event Func<string, JToken, Task> UnknownDispatchReceived
+        {
+            add => _unknownDispatchReceived.Add(value);
+            remove => _unknownDispatchReceived.Remove(value);
+        }
+
+        internal readonly AsyncEvent<Func<string, JToken, Task>> _unknownDispatchReceived = new();
+
+        #endregion
     }
 }

src/Discord.Net.WebSocket/DiscordSocketClient.EventHandling.cs

@@ -2506,6 +2506,8 @@ private async Task ProcessMessageAsync(GatewayOpCode opCode, int? seq, string ty
                         default:
                             if (!SuppressUnknownDispatchWarnings)
                                 await _gatewayLogger.WarningAsync($"Unknown Dispatch ({type})").ConfigureAwait(false);
+
+                            await TimedInvokeAsync(_unknownDispatchReceived, nameof(UnknownDispatchReceived), type, (payload as JToken));
                             break;
                             #endregion
                     }