Rename password_form_had_username_field to more appropriate

Naming of `password_form_had_username_field` doesn't show that the
usernames outside and inside the password form are matching.

With the work on UFF with intermediate fields, it makes more sense
to signify the `matching` part of the usernames.


Pure renaming, no logic change.

Bug: 1470586
Change-Id: Ic1c46c2fee99e6316a9d627c83121c5a3ebc5487
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4859725
Reviewed-by: Maxim Kolosovskiy <kolos@chromium.org>
Commit-Queue: Din Nezametdinov <shaikhitdin@google.com>
Cr-Commit-Position: refs/heads/main@{#1196129}