[ios] Add helpers to manual fill to unlock credit cards

These helpers create a bridge between manual fill credit card and
payments' FullCardRequester to let user 'unlock' server side credit card
by entering correct cvc.

Bug: 845472
Change-Id: I9fcf013a0352673659d77291c03faa8aa31a9980
Reviewed-on: https://chromium-review.googlesource.com/c/1304413
Reviewed-by: Eric Noyau <noyau@chromium.org>
Reviewed-by: Moe Ahmadi <mahmadi@chromium.org>
Commit-Queue: David Jean <djean@chromium.org>
Cr-Commit-Position: refs/heads/master@{#606382}
6 files changed