types(Partial): add partial reactions (#6066)

Co-authored-by: Noel <buechler.noel@outlook.com>

src/structures/Channel.js

@@ -63,6 +63,16 @@ class Channel extends Base {
     return new Date(this.createdTimestamp);
   }
 
+  /**
+   * Whether this Channel is a partial
+   * <info>This is always false outside of DM channels.</info>
+   * @type {boolean}
+   * @readonly
+   */
+  get partial() {
+    return false;
+  }
+
   /**
    * When concatenated with a string, this automatically returns the channel's mention instead of the Channel object.
    * @returns {string}

src/structures/DMChannel.js

@@ -16,8 +16,10 @@ class DMChannel extends Channel {
    */
   constructor(client, data) {
     super(client, data);
+
     // Override the channel type so partials have a known type
     this.type = 'DM';
+
     /**
      * A manager of the messages belonging to this channel
      * @type {MessageManager}

src/structures/GuildMember.js

@@ -65,7 +65,7 @@ class GuildMember extends Base {
     if ('user' in data) {
       /**
        * The user that this guild member instance represents
-       * @type {User}
+       * @type {?User}
        */
       this.user = this.client.users._add(data.user, true);
     }

src/structures/Message.js

@@ -388,7 +388,7 @@ class Message extends Base {
   /**
    * The message contents with all mentions replaced by the equivalent text.
    * If mentions cannot be resolved to a name, the relevant mention in the message content will not be converted.
-   * @type {string}
+   * @type {?string}
    * @readonly
    */
   get cleanContent() {