[VCN] Move CVC unmask prompt functions to payments client

No-op change. Only refactoring.

The PaymentsRpcResult and PaymentsCardType could also be moved but
ideally in separate CLs to avoid touching too many files in this CL.

Bug: 40937065, 303715512
Change-Id: I435b9d7b9f627e337aa4103b16ac1f757597c33b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5411451


Reviewed-by: Christoph Schwering <schwering@google.com>
Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Commit-Queue: Siyu An <siyua@chromium.org>
Reviewed-by: Vinny Persky <vinnypersky@google.com>
Cr-Commit-Position: refs/heads/main@{#1282704}