Wrong claim format designation in presentation submission

[rmnre]

When issuing a presentation of a W3C verifiable credential, the "format" property in the Input Descriptor Mapping Object of the presentation submission is currently being set to "ldp_vp". It must be set to "ldp_vc" instead, as it refers to the format of the enclosed credential. (See https://identity.foundation/presentation-exchange/spec/v1.0.0/#presentation-submission)

The parts that need to be changed to produce correct presentation submissions are here:
https://github.com/hyperledger/aries-cloudagent-python/blob/4240fa9b192ea4cdb4026211ea4bec694aec5506/aries_cloudagent/protocols/present_proof/dif/pres_exch_handler.py#L1357-L1361

and here (maybe just remove the default entirely?):
https://github.com/hyperledger/aries-cloudagent-python/blob/4240fa9b192ea4cdb4026211ea4bec694aec5506/aries_cloudagent/protocols/present_proof/dif/pres_exch.py#L835-L840

However, verification logic might also need some adaptations when this parameter is changed, I haven't looked into that yet.