fix: Gateway events for DMs (#1854)

* Fix MessageUpdate when there's no channel cached

* Fix message events

* Fix cacheable type

* Fix examples

* Revert MessageUpdated

src/Discord.Net.WebSocket/API/Gateway/Reaction.cs

@@ -10,6 +10,8 @@ namespace Discord.API.Gateway
         public ulong MessageId { get; set; }
         [JsonProperty("channel_id")]
         public ulong ChannelId { get; set; }
+        [JsonProperty("guild_id")]
+        public Optional<ulong> GuildId { get; set; }
         [JsonProperty("emoji")]
         public Emoji Emoji { get; set; }
         [JsonProperty("member")]