feat(Util): added formatters

[kyranet]

Please describe the changes this PR makes and why it should be merged:

ref: #5918

Usage:

const { Formatters } = require('discord.js');

Formatters.bold('Hello there');
// **Hello there**

const { Formatters: { bold, italic } } = require('discord.js');

bold(italic('General Kenobi!'));
// **_General Kenobi!_**

Or with TypeScript / ESM:

import { Formatters } from 'discord.js';

Formatters.codeBlock('You are a bold one.');
// ```\nYou are a bold one.```

Note: A namespace was used because it's the equivalent of export * as Formatters from './util/Formatters'; in TypeScript.

Status and versioning classification:

• Code changes have been tested against the Discord API, or there are no code changes
• I know how to update typings and have done so, or typings don't need updating
• This PR changes the library's interface (methods or parameters added)