[Spec] =compute the key hash of reporting ID= uses wrong prefix for buyerAndSellerReportingId and buyerReportingId

[brusshamilton]

=compute the key hash of a reporting ID= always uses "NameReport" as the prefix of the k-anonymity key. When the buyerAndSellerReportingId is used the prefix should be "BuyerAndSellerReportId". Likewise when the buyerReportingId is used the prefix should be "BuyerReportId".

These need to be counted separately because they guard separate fields in reporting. If they were counted together for k-anonymity purposes, additional information could be leaked based on which field was populated.