Settings: Introduce "limited sharing" mechanism.

This mechanism will be used to share files between CrOS and Browser
Settings, in an effort to properly decouple these UIs code.

In this CL moving only a single file to the sharing mechanism as an
example. Remaining shared files will be moved in follow-ups.

Bug: 1431477
Change-Id: Icfbaf7fe23aa474b9ccca66c14f2e5fa693358f2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4408104
Reviewed-by: Xiaohui Chen <xiaohuic@chromium.org>
Reviewed-by: John Lee <johntlee@chromium.org>
Commit-Queue: Demetrios Papadopoulos <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1130155}