[Android][CredMan][Mfill] Prevent Reentry-point on unqualified fields

The chip that allows to finish a CredMan sign-in shows on any field as
long as the sign-in is pending. When focusing a field that is not marked
as related to signin (i.e. password, username, or new: webauthn), the
reentry point should be hidden.
This prevents confusion (e.g. when focusing search fields) and allows to
use the space in the accessory for more relevant suggestions.

Bug: 1444418
Change-Id: I32977a1a62b1130dd24558d1b8c105a33afea9e7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4542643


Reviewed-by: Mike West <mkwst@chromium.org>
Reviewed-by: Maxim Kolosovskiy <kolos@chromium.org>
Commit-Queue: Friedrich Horschig <fhorschig@chromium.org>
Reviewed-by: Mohamed Amir Yosef <mamir@chromium.org>
Code-Coverage: Findit <findit-for-me@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#1148489}