hash Code
Calculates a hash code value for the current W3CCredential
object.
The hash code is generated by combining the hash codes of the following properties:
id
credentialType
context
type
issuer
issuanceDate
expirationDate
credentialSchema
credentialSubject
credentialStatus
refreshService
evidence
termsOfUse
validFrom
validUntil
proof
aud
Return
The calculated hash code value.