Media types do not indicate securing mechanism

[msporny]

Originally posted by @Sakurann in #1062 (comment)

media types do not indicate proofing mechanisms

I think we should apply the same philosophy to all media types related to this specification that media types describe a secured 'thing' and media type itself does not imply the proofing mechanism. given the base media type is application/vc+ld+json; all extensions of VCDM core spec should use vc+.

[TallTed]

Rather, I would say that media types describe a securable 'thing' or media types describe a possibly secured 'thing'.

That is to say — as with a password-secured ZIP, or a signed and/or encrypted email message — the structure is defined by the media type and allows for signature or encryption, but the content does not necessarily include either signature or encryption.

[Sakurann]

might be more in-scope fo vc-jwt spec. but needs guidance that this media type is to be used as cty not typ JOSE Header.

[brentzundel]

I've attempted to capture the language and ideas above in PR #1107, please review.