feat: deprecate GuildEmbed methods and properties in favour of GuildWidget

[NotSugden]

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

This PR deprecates all of the methods and properties relating to GuildEmbed as its deprecated from the API (see discord/discord-api-docs#1536), and adds in new methods fetchWidget and setWidget

I wasn't sure whether to change the existing methods to use the widget endpoint since the methods are deprecated, the new methods should instead be used (although it will eventually lead to the old methods breaking)

I also thought it better to rename the existing typedefs (as that's not breaking since the return types are still the same) instead of making duplicate typedefs

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.

[advaith1]

My relevant upstream API docs PR has been merged.

[SpaceEEC]

Just small nits about the @deprecated annotations.

[advaith1]

The deprecated guild embed properties and endpoints are removed in API v8.

Resolved

[advaith1]

just realized, would it be a good idea to document the replacements in the descriptions?

[iCrawl]

We did not do that in the past.