[Save and Fill] Implement card validation feedback

This change introduces new logic to the SaveAndFillDialog to provide
real-time validation feedback for card number input.

key changes:
1. Dynamic Error Message Display: Added logic to
dynamically display an error message when the entered credit card number
is invalid. This message appears and disappears as the user types,
leveraging the existing IsValidCreditCardNumber validation logic.

2. Stable Dialog Height: Introduced a padding view that hides and shows,
ensuring the dialog's height remains constant. This prevents the dialog
from unexpectedly shifting or stretching when the error message appears
or disappears.

Mocks: https://screenshot.googleplex.com/76zVhv6cb9MV4Ci.png (note:
labels are missing in this mock)
Implementation:
https://screencast.googleplex.com/cast/NDU1MzMzNTQ5MDIxNTkzNnwzZjg4MGU1Ny0xZg

Bug: 378165002, 378163937
Change-Id: Ib28354988d597372a3fd1cb004e8d6bca91305fd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6574236
Reviewed-by: Siyu An <siyua@chromium.org>
Commit-Queue: Verina Armanyous <averina@google.com>
Reviewed-by: Mohamed Amir Yosef <mamir@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1471948}