[Password Manager] Improve add password dialog

This change updates error message for empty website, and highlights
password field as invalid after leaving it empty.

Bug: 1398560
Change-Id: I0beb0024aafacf70d74cacb635a3c46335aea232
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4376775


Reviewed-by: Mohamed Amir Yosef <mamir@chromium.org>
Commit-Queue: Viktor Semeniuk <vsemeniuk@google.com>
Cr-Commit-Position: refs/heads/main@{#1123201}