match inherited vcts with credential_type for SD-JWT VC

[jogu]

The SD-JWT VC annex (from #22) currently says a CredentialQuery matches SD-JWT VCs whose vct is identical to credential_type (case-sensitive text comparison). OpenID4VP's vct_values is looser: "The Wallet MAY return Credentials that inherit from any of the specified types, following the inheritance logic defined in SD-JWT VC".

We need to decide whether DCHP:

• requires exact vct equality (simple, predictable, no type-metadata resolution needed on the wallet);
• allow matching against aka_vcts too ( https://www.ietf.org/archive/id/draft-ietf-oauth-sd-jwt-vc-19.html#name-other-credential-types-aka_ )
• allows or requires matching on inherited types, in which case the wallet needs the type metadata chain at matching time;
• leaves this to the credential format definition / ecosystem.

Related to #46 (making credential_type an array), since both concern what credential_type matches. The annex added for #22 carries an editor's note pointing at this question.