Add newly_created bool field to the ThreadCreate event (#3084)

https://discord.com/developers/docs/events/gateway-events#thread-create

Author: jamesbt365

src/gateway/client/dispatch.rs

@@ -420,6 +420,7 @@ fn update_cache_with_event(
 
             FullEvent::ThreadCreate {
                 thread: event.thread,
+                newly_created: event.newly_created,
             }
         },
         Event::ThreadUpdate(mut event) => {

src/gateway/client/event_handler.rs

@@ -411,8 +411,8 @@ event_handler! {
 
     /// Dispatched when a thread is created or the current user is added to a private thread.
     ///
-    /// Provides the thread.
-    ThreadCreate { thread: GuildChannel } => async fn thread_create(&self, ctx: Context);
+    /// Provides the thread and if the thread was newly created.
+    ThreadCreate { thread: GuildChannel, newly_created: Option<bool> } => async fn thread_create(&self, ctx: Context);
 
     /// Dispatched when a thread is updated.
     ///

src/model/event.rs

@@ -861,10 +861,11 @@ pub struct StageInstanceDeleteEvent {
 /// [Discord docs](https://discord.com/developers/docs/topics/gateway-events#thread-create).
 #[cfg_attr(feature = "typesize", derive(typesize::derive::TypeSize))]
 #[derive(Clone, Debug, Deserialize, Serialize)]
-#[serde(transparent)]
 #[non_exhaustive]
 pub struct ThreadCreateEvent {
+    #[serde(flatten)]
     pub thread: GuildChannel,
+    pub newly_created: Option<bool>,
 }
 
 /// Requires [`GatewayIntents::GUILDS`].