feat(cleanContent): add missing emojis & slash mentions

[DraftProducts]

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

The function <Util>.cleanContent function replace all mentions by the text equivalent. This PR add the two missing mentions types :

• Commands mentions: </command:318312854816161792>.
• Custom emojis mentions: <:emoji:318312854816161792>.

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

[vercel[bot]]

The latest updates on your projects. Learn more about Vercel for Git ↗︎

Name	Status	Preview	Comments	Updated
discord-js	✅ Ready (Inspect)	Visit Preview	💬 Add your feedback	Mar 26, 2023 at 4:34AM (UTC)
discord-js-guide	✅ Ready (Inspect)	Visit Preview	💬 Add your feedback	Mar 26, 2023 at 4:34AM (UTC)

[jaw0r3k]

:name: doesnt look like a proper way to show an emoji

[DraftProducts]

:name doesnt look like a proper way to show an emoji

Discord render emojis like that : :name:

[jaw0r3k]

Discord render emojis like that : :name:

Then nvm

[vercel[bot]]

@DraftProducts is attempting to deploy a commit to the discordjs Team on Vercel.

A member of the Team first needs to authorize it.

[github-actions[bot]]

⚡️ Lighthouse report for the changes in this PR:

Category	Score
🟠 Performance	75
🟢 Accessibility	94
🟢 Best practices	100
🟢 SEO	100
🟠 PWA	70

Lighthouse ran on https://discord-js-git-fork-draftbot-clean-content-mentions-discordjs.vercel.app/

[DraftProducts]

My apologies for forgetting and abandoning PR; strangely enough, I don't seem to have received any notification of the answer or milestone changes 🤔