Implement cancelling card unmask authentication selection on iOS.

Before tapping the cancel button did nothing. Now, the card unmask
authentication selection bottom sheet is dismissed (and metrics are
logged).

Screencap: https://drive.google.com/file/d/1tu5euQcOFQEHD6EMYDQcWRuCklW8P2Qk/view?usp=sharing&resourcekey=0-nE9pkf01wdbFCGSdl3XyiQ

Bug: 40282545, b/324887950
Change-Id: Ia8466af593094236dd5529c11405628cd7f10066
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5402067


Reviewed-by: Siyu An <siyua@chromium.org>
Reviewed-by: Tommy Martino <tmartino@chromium.org>
Commit-Queue: Slobodan Pejic <slobodan@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1283376}