Support Embed and new Attachment flags

[Snipy7374]

Summary

Embed and Attachment API is outdated

What is the feature request for?

The core library

The Problem

Embed and Attachment API is outdated; new flags will be released soon:

discord/discord-api-docs#7353

The Ideal Solution

Update the Embed and Attachment APIs

The Current Solution

No response

Additional Context

No response

[onerandomusername]

Much as the API docs never got merged, I have no qualms about implementing this because these flags ARE implemented in the client, and it can be implemented in a way that if they are removed, the client won't break.