docs: add extends to ChannelManager, cache is not nullable, resolveID accepts an object (#3771)

* Add extends to docs

* Cache shouldn't be nullable

* jsdoc: use same type for both resolve methods

src/managers/BaseManager.js

@@ -35,7 +35,7 @@ class BaseManager {
 
     /**
     * Holds the cache for the data model
-    * @type {?Collection}
+    * @type {Collection}
     */
     this.cache = new cacheType(...cacheOptions);
     if (iterable) for (const i of iterable) this.add(i);
@@ -64,7 +64,7 @@ class BaseManager {
 
   /**
    * Resolves a data entry to a instance ID.
-   * @param {string|Instance} idOrInstance The id or instance of something in this Manager
+   * @param {string|Object} idOrInstance The id or instance of something in this Manager
    * @returns {?Snowflake}
    */
   resolveID(idOrInstance) {

src/managers/ChannelManager.js

@@ -6,6 +6,7 @@ const { Events } = require('../util/Constants');
 
 /**
  * A manager of channels belonging to a client
+ * @extends {BaseManager}
  */
 class ChannelManager extends BaseManager {
   constructor(client, iterable) {