feat(Webhook): add '(edit|delete)Message' methods

[izexi]

Adds support for the Edit Webhook Message and Delete Webhook Message endpoints.

After #4876 is merged, the object that represents the raw message data in the typings can be replaced to be more accurate with either WebhookRawMessageResponse (or eventually APIMessage over on discord-api-types). (See df89d04)

Here's a snippet of how I tested these changes

import { once } from 'events';
import { TOKEN } from './constants';
import { APIMessage, Client, MessageEmbed, WebhookClient } from 'discord.js';

const client = new Client();
let guild, webhook, message;

beforeAll(async (done) => {
  client.login(TOKEN);
  await once(client, 'ready');

  guild = await client.guilds.create('guild');
  webhook = await guild.channels.cache.find(({ type }) => type === 'text').createWebhook('webhook');
  message = await webhook.send('message');

  done();
});

test('calling Webhook#editMessage() on a cached message should return the updated Message', async () => {
  const content = 'foo';
  const embeds = [new MessageEmbed().setDescription('foo'), new MessageEmbed().setDescription('bar')];

  await expect(webhook.editMessage(message, content, { embeds })).resolves.toMatchObject({ content, embeds });
});

test('calling Webhook#editMessage() on an uncached message should return the updated Message', async () => {
  const content = 'bar';
  message.channel.messages.cache.delete(message.id);

  await expect(webhook.editMessage(message, content)).resolves.toMatchObject({ content });
});

test('calling Webhook#editMessage() with an APIMessage|MessageEmbed|MessageEmbed[] as the 2nd param', async () => {
  const content = 'foo';
  const embed = new MessageEmbed().setDescription('foo');
  const embeds = [embed, embed.setDescription('bar')];

  await expect(webhook.editMessage(message, APIMessage.create(webhook, content))).resolves.toMatchObject({ content });
  await expect(webhook.editMessage(message, embed)).resolves.toMatchObject({ embeds: [embed] });
  await expect(webhook.editMessage(message, embeds)).resolves.toMatchObject({ embeds });
});

test('calling Webhook#editMessage() with files', async () => {
  const url = 'https://cdn.discordapp.com/avatars/191615925336670208/a_594885c678ec070375a459e56c623dbd.gif?size=4096';
  const { attachments } = await webhook.editMessage(message.id, { files: [url] });

  await expect(attachments.size === 1);
  await expect(attachments.first().url === url);
});

test('calling Webhook#editMessage() on a message that belongs to an uncached channel or WebhookCliet#editMessage() should return the raw message data', async () => {
  client.channels.remove(message.channel.id);

  await expect(webhook.editMessage(message.id, 'baz')).resolves.toMatchObject({ type: 0 });
  await expect(new WebhookClient(webhook.id, webhook.token).editMessage(message.id, 'qux')).resolves.toMatchObject({
    type: 0,
  });
});

test('calling Webhook#deleteMessage() and then fetching the deleted message should reject with an error', async () => {
  await webhook.deleteMessage(message);

  await expect(message.fetch(true)).rejects.toThrow('Unknown Message');
});

afterAll(() => guild.delete());

Status

• 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

Semantic versioning classification:

• This PR changes the library's interface (methods or parameters added)
  • This PR includes breaking changes (methods removed or renamed, parameters moved or removed)
• This PR only includes non-code changes, like changes to documentation, README, etc.

[SpaceEEC]

This PR probably needs a rebase, I suspect that the duplicated type is from this PR and #4876.
Th merge commit as of now: 45adb3b#diff-4f45caa500ef03d94d3c2bfa556caa1642df95d4e2b980d76b876a8fd2e8c522R3349

[izexi]

Added the option to allow APIMessage as the 2nd param to be consistent with send() and other message editing methods and also MessageEmbed/MessageEmbed[] can be accepted as the 2nd param since APIMessage#resolveData() can handle that.

Code used to test this change (which has also been added within the test code in the PR description)

test('calling Webhook#editMessage() with an APIMessage|MessageEmbed|MessageEmbed[] as the 2nd param', async () => {
  const content = 'foo';
  const embed = new MessageEmbed().setDescription('foo');
  const embeds = [embed, embed.setDescription('bar')];

  await expect(webhook.editMessage(message, APIMessage.create(webhook, content))).resolves.toMatchObject({ content });
  await expect(webhook.editMessage(message, embed)).resolves.toMatchObject({ embeds: [embed] });
  await expect(webhook.editMessage(message, embeds)).resolves.toMatchObject({ embeds });
});

[advaith1]

Attachments can be uploaded when editing a webhook message (discord/discord-api-docs#2615 (comment), discord/discord-api-docs#2615 (comment))

[izexi]

Added the option to edit the message with files (ref: discord/discord-api-docs#2720)

Code used to test this change (which has also been added within the test code in the PR description)

test('calling Webhook#editMessage() with files', async () => {
  const url = 'https://cdn.discordapp.com/avatars/191615925336670208/a_594885c678ec070375a459e56c623dbd.gif?size=4096';
  const { attachments } = await webhook.editMessage(message.id, { files: [url] });

  await expect(attachments.size === 1);
  await expect(attachments.first().url === url);
});