feat: add support for guild forums (#7791)

* feat: add support for guild forums

* feat(webhook): add support for creating forum channel posts

* fix: duplicated docs

* feat: add support for message counts

* feat: add support for latest upstream changes

* fix: serialize forum channels

* types: fix channel unions

* types: fix tests

* types: fix tests (again)

* types: fix tests (again (again))

* chore: make requested changes

* chore: fix bugs and make requested changes

* types: use correct type for guild forum start messages

* chore: remove console.log

* chore: make requested changes

* chore: make requested changes

* chore: fix docs

* Update packages/discord.js/src/managers/GuildForumThreadManager.js

Co-authored-by: Jiralite <33201955+Jiralite@users.noreply.github.com>

* chore: update types

* chore: make requested changes

* chore: Apply suggestions

Co-authored-by: Jaworek <jaworekwiadomosci@gmail.com>
Co-authored-by: Jonathan Rubenstein <jrubcop@gmail.com>

* fix: import `ErrorCodes`

* fix: remove defunct code

* refactor: be consistent with channel class names

* feat(GuildChannel): add flags

* fix: rename file

* refactor: channel flags are everywhere!

* fix: import flags correctly

* chore(ThreadChannel): update message count string

* docs(Channels): correct `@param` type

* docs(Channels): ignore transformGuildDefaultReaction

* refactor: emoji object in tags

* chore: renaming consistency

* fix: document default reaction emojis in patching

* fix(GuildChannelManager): document `defaultThreadRateLimitPerUser`

* chore: semicolon

* docs(ErrorCodes): document `GuildForumMessageRequired`

* refactor: transform default reactions

* docs(APITypes): Add `ChannelFlags`

* fix: convert tags properly

* fix: pass an array of snowflakes

* refactor: handle flags better

* fix(ThreadChannel): receive tags

* fix(PartialGroupDMChannel): nullify `flags`

Apparently did not do this earlier.

* chore: misc sorting

* refactor: nullify emoji on tags if not present

* refactor(ForumChannel): modify returns

* types: protect the thread manager!

Co-authored-by: SpaceEEC <spaceeec@yahoo.com>

* chore: update `ChannelType` usage

* Update index.d.ts

* docs: Update default reaction emoji property names

Co-authored-by: Almeida <almeidx@pm.me>

* fix: only `name` is required when editing tags

- discord/discord-api-docs#5458

* types: add tests for `channel.flags`

* fix: allow unsetting the default reaction emoji

* refactor: remove v13 remnants

* docs: add missing closing tag

* feat: add `rateLimitPerUser`

* feat: add missing properties for create guild channel

- discord/discord-api-docs#5474

* refactor(GuildForumThreadManager): refactor message payload

* fix: handle magical `null` case

Co-authored-by: A. Román <kyradiscord@gmail.com>

Co-authored-by: Jiralite <33201955+Jiralite@users.noreply.github.com>
Co-authored-by: Jaworek <jaworekwiadomosci@gmail.com>
Co-authored-by: Jonathan Rubenstein <jrubcop@gmail.com>
Co-authored-by: SpaceEEC <spaceeec@yahoo.com>
Co-authored-by: Almeida <almeidx@pm.me>
Co-authored-by: A. Román <kyradiscord@gmail.com>

packages/discord.js/src/structures/Message.js

@@ -187,6 +187,17 @@ class Message extends Base {
       this.stickers = new Collection(this.stickers);
     }
 
+    if ('position' in data) {
+      /**
+       * A generally increasing integer (there may be gaps or duplicates) that represents
+       * the approximate position of the message in a thread.
+       * @type {?number}
+       */
+      this.position = data.position;
+    } else {
+      this.position ??= null;
+    }
+
     // Discord sends null if the message has not been edited
     if (data.edited_timestamp) {
       /**
@@ -800,7 +811,7 @@ class Message extends Base {
 
   /**
    * Create a new public thread from this message
-   * @see ThreadManager#create
+   * @see GuildTextThreadManager#create
    * @param {StartThreadOptions} [options] Options for starting a thread on this message
    * @returns {Promise<ThreadChannel>}
    */