[Payments] Move focus to next field in expired cvc unmask prompt.
Moves the focus to the expiration year field when the expiration month
field gets filled with a second character and move the focus to the
cvc input field when the expiration year field gets filled with a
second character.
Also adds more detailed error messages for invalid expiration month and
year.
BUG=671762
Review-Url: https://codereview.chromium.org/2557873002
Cr-Commit-Position: refs/heads/master@{#437571}
4 files changed
