[iOS] Update Best Features strings

This change updates the string
IDS_IOS_BEST_FEATURES_PASSWORDS_IN_OTHER_APPS_STEP_3_AUTOFILL_SETTINGS
to match the text used by Apple. IDS_IOS_BEST_FEATURES_LENS_TITLE is
also moved to ios_strings.grd to follow the guidance on how strings
referring to Google Lens should be handled.

Fixed: 408018343
Change-Id: If8b763dfc5c4e0ce3ad82991fda5bcb765800bb6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6935025
Reviewed-by: Hira Mahmood <hiramahmood@google.com>
Commit-Queue: Briana McClure <bmcclure@google.com>
Cr-Commit-Position: refs/heads/main@{#1513902}