Accept all three representations of the Public collection

[acid-chicken]

Summary

https://github.com/syuilo/misskey/blob/9e20fc5c88683d92a0bd9aade4ef6085bfb27e8c/src/remote/activitypub/models/note.ts#L117-L118

NOTE

Compacting an ActivityStreams object using the ActivityStreams JSON-LD context might result in https://www.w3.org/ns/activitystreams#Public being represented as simply Public or as:Public which are valid representations of the Public collection. Implementations which treat ActivityStreams objects as simply JSON rather than converting an incoming activity over to a local context using JSON-LD tooling should be aware of this and should be prepared to accept all three representations.
— 5.6 Public Addressing - ActivityPub