Fix PWM manual fallback metrics emission

Problem: When a field filled via autofill, it is setting the incorrect
mask property value.

This fix makes sure that a more granular value is used, which leads to
a fix to a metric that is emitted in password manager.

Another small issue fixed in the CL is a type on the metrics enum.
This change is ok because the incorrect bucket "9" will simply
disappear as we stop emitting values to it.

Bug: 379822177
Change-Id: I40dd7adf9afd053053ce92070e951ed2eb42299d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6032056
Reviewed-by: Christoph Schwering <schwering@google.com>
Reviewed-by: Jihad Hanna <jihadghanna@google.com>
Commit-Queue: Bruno Braga <brunobraga@google.com>
Reviewed-by: Maria Kazinova <kazinova@google.com>
Code-Coverage: findit-for-me@appspot.gserviceaccount.com <findit-for-me@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#1384901}