Using `id` that is not an URI in AnonCreds credential issue due to transformation to/from W3C class

[TimoGlastra]

The W3C credential class validates that credenitalSubject.id is an URI, according to the spec. This is fine if you want to use AnonCred with W3C format, however if you had legacy AnonCreds credentials containing an id property that is not an URI, this is now causing issues as we internally transform the anoncreds credential to w3c format, even if you're not using the w3c format at all.

As reported by @sairanjit in discord

FYI @swcurran interesting edge case we hadn't thought of

@auer-martin is going to pick this up