Update SIOP/OpenId4VP implementation

Created by: nodh

Several issues came up after integration testing with EUDIW:

• Need to implement https://openid.net/specs/openid-4-verifiable-presentations-1_0.html#name-response-mode-direct_postjw
• Need to reconsider supporting client_id_scheme
• Need to support loading public keys from a JWKS, referenced by kid in the JWS header, when calling VerifierJwsService.verifyJwsObject(string)
• Refactor AuthenticationResponseResult.Post to contain the parameter keys and values instead of directly encoding them, so clients can correctly post that to the SIOP verifier