docs: describe private properties (#8879)

* feat: describe private properties

* Update packages/discord.js/src/structures/GuildMember.js

Co-authored-by: MrMythicalYT <91077061+MrMythicalYT@users.noreply.github.com>

* Apply suggestions from code review

Co-authored-by: MrMythicalYT <91077061+MrMythicalYT@users.noreply.github.com>

* Apply suggestions from code review

---------

Co-authored-by: MrMythicalYT <91077061+MrMythicalYT@users.noreply.github.com>
Co-authored-by: kodiakhq[bot] <49736102+kodiakhq[bot]@users.noreply.github.com>

packages/discord.js/src/managers/CachedManager.js

@@ -11,6 +11,13 @@ class CachedManager extends DataManager {
   constructor(client, holds, iterable) {
     super(client, holds);
 
+    /**
+     * The private cache of items for this manager.
+     * @type {Collection}
+     * @private
+     * @readonly
+     * @name CachedManager#_cache
+     */
     Object.defineProperty(this, '_cache', { value: this.client.options.makeCache(this.constructor, this.holds) });
 
     if (iterable) {

packages/discord.js/src/structures/GuildMember.js

@@ -54,6 +54,11 @@ class GuildMember extends Base {
      */
     this.communicationDisabledUntilTimestamp = null;
 
+    /**
+     * The role ids of the member
+     * @type {Snowflake[]}
+     * @private
+     */
     this._roles = [];
     if (data) this._patch(data);
   }

packages/discord.js/src/structures/Presence.js

@@ -141,6 +141,12 @@ class Presence extends Base {
  */
 class Activity {
   constructor(presence, data) {
+    /**
+     * The presence of the Activity
+     * @type {Presence}
+     * @readonly
+     * @name Activity#presence
+     */
     Object.defineProperty(this, 'presence', { value: presence });
 
     /**
@@ -287,6 +293,12 @@ class Activity {
  */
 class RichPresenceAssets {
   constructor(activity, assets) {
+    /**
+     * The activity of the RichPresenceAssets
+     * @type {Activity}
+     * @readonly
+     * @name RichPresenceAssets#activity
+     */
     Object.defineProperty(this, 'activity', { value: activity });
 
     /**