docs: Add/normalize .toString() docs on all classes (#2042)

* docs: Add/normalize .toString() examples on all classes

* docs: Remove exclamation point on ClientApplication#toString example

* docs: Normalize .toString() descriptions on all classes

* Use "returns" instead of "concatenates"

src/structures/GuildChannel.js

@@ -493,11 +493,8 @@ class GuildChannel extends Channel {
    * When concatenated with a string, this automatically returns the channel's mention instead of the Channel object.
    * @returns {string}
    * @example
-   * // Outputs: Hello from #general
-   * console.log(`Hello from ${channel}`);
-   * @example
-   * // Outputs: Hello from #general
-   * console.log('Hello from ' + channel);
+   * // Logs: Hello from <#123456789012345678>!
+   * console.log(`Hello from ${channel}!`);
    */
   toString() {
     return `<#${this.id}>`;