Workaround: 'as:Public' not recognized by many implementations

[alphatownsman]

Many implementations, e.g. Pleroma and many relays, do not recognize as:Public, but only know https://www.w3.org/ns/activitystreams#Public in to/cc for public posts, some also does not accept to/cc unless it's list. This causes public posts from Takahe being rejected or ignored.

This patches outbound json to use full uri instead of as:Public. This is more of hack than a proper implementation.

There are other implementation doing this too. https://github.com/jaywink/federation/blob/e0592e17d006b3f32bdec8baaed6a31ffbc7ade1/federation/entities/activitypub/ldcontext.py#L58

Suggestions and improvements are welcomed.

[andrewgodwin]

The correct way to do this is to instead change the context that the JSON-LD canonicaliser uses, to remove the "as:Public" short identifer - that way the JSON-LD library will leave it expanded.