Partials (#3070)

* Remove GroupDMChannels

they sparked no joy

* Start partials for message deletion

* MessageUpdate partials

* Add partials as an opt-in client option

* Add fetch() to Message

* Message.author should never be undefined

* Fix channels being the wrong type

* Allow fetching channels

* Refactor and add reaction add partials

* Reaction remove partials

* Check for emoji first

* fix message fetching

janky

* User partials in audit logs

* refactor overwrite code

* guild member partials

* partials as a whitelist

* document GuildMember#fetch

* fix: check whether a structure is a partial, not whether cache is true

* typings: Updated for latest commit (#3075)

* partials: fix messageUpdate behaviour (now "old" message can be partial)

* partials: add warnings and docs

* partials: add partials to index.yml

* partials: tighten "partial" definitions

* partials: fix embed-only messages counting as partials

src/structures/Guild.js

@@ -5,7 +5,7 @@ const Integration = require('./Integration');
 const GuildAuditLogs = require('./GuildAuditLogs');
 const Webhook = require('./Webhook');
 const VoiceRegion = require('./VoiceRegion');
-const { ChannelTypes, DefaultMessageNotifications, browser } = require('../util/Constants');
+const { ChannelTypes, DefaultMessageNotifications, PartialTypes, browser } = require('../util/Constants');
 const Collection = require('../util/Collection');
 const Util = require('../util/Util');
 const DataResolver = require('../util/DataResolver');
@@ -341,7 +341,9 @@ class Guild extends Base {
    * @readonly
    */
   get owner() {
-    return this.members.get(this.ownerID) || null;
+    return this.members.get(this.ownerID) || (this.client.options.partials.includes(PartialTypes.GUILD_MEMBER) ?
+      this.members.add({ user: { id: this.ownerID } }, true) :
+      null);
   }
 
   /**