[Android][Mfill][CredMan] Add Passkeys to Fallback sheet

With this CL, the password accessory controller sends the username and
the ID of each Passkey stored in GMS Core to the filling controller.

The method to fill in any other fallback sheet isn't used yet but since
the standard allows for other documents like driving licenses, it's not
worth special casing this.

https://crrev.com/c/4831795 then renders the Passkey as chip as shown
in the mock in crbug.com/1477267#c1.

It cleans up a couple of unused includes.

Low-Coverage-Reason: Underreported, see crbug.com/1477561.
Bug: 1477267
Change-Id: If70423ab69d8ae87c3f1f8db6af0ceb34438f17b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4827526
Commit-Queue: Friedrich Horschig <fhorschig@chromium.org>
Reviewed-by: Florian Leimgruber <fleimgruber@google.com>
Reviewed-by: Ioana Pandele <ioanap@chromium.org>
Reviewed-by: Maxim Kolosovskiy <kolos@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1192414}