[Uno-D] Revamp ChromeSignin Setting + String updates

Changed the setting from radio buttons to a list selection.
Empty choice shows a "Select an option" placeholder that is not a
selectable option. Once the user chooses, it cannot be chosen again.

String updates added as well.

Screenshot: https://screenshot.googleplex.com/3xSEQ3wMTFsTXnA

Bug: b:345160198
Change-Id: I3826b39acdf5f477e9a9df666d02a659d222a1b4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5604490
Reviewed-by: David Roger <droger@chromium.org>
Code-Coverage: findit-for-me@appspot.gserviceaccount.com <findit-for-me@appspot.gserviceaccount.com>
Commit-Queue: Ryan Sultanem <rsult@google.com>
Cr-Commit-Position: refs/heads/main@{#1311826}