Log metrics for Save Card Infobar Banner on iOS. (1/2)

This CL uses the new method
(autofill::autofill_metrics::LogSaveCreditCardPromptResultIOS) to
specifically record when Save Card infobar “Banner" is shown and
accepted by the user.

Before this CL, logging generic
`autofill::AutofillMetrics::InfoBarMetric` lacked the ability to
differentiate between Infobar Banner and Modal overlays and their
outcomes. Additionally, the acceptance of the banner was not recorded.

Bug: 394337041, 396707203
Change-Id: Ia384ba3696300cb38487a17aa5373bb769190157
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6235365
Commit-Queue: Kavita Soni <kavitasoni@chromium.org>
Reviewed-by: Vincent Boisselle <vincb@google.com>
Reviewed-by: Mike Dougherty <michaeldo@chromium.org>
Reviewed-by: Sergio Collazos <sczs@chromium.org>
Reviewed-by: Slobodan Pejic <slobodan@chromium.org>
Reviewed-by: Rouslan Solomakhin <rouslan@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1421571}