[FilesBulkPinning] Expose drive shortcuts via a CSS class in Files app

Shortcut identification has been plumbed through from DriveFS and
available on ToT. This plumbs through shortcuts that are user accessible
to Files app UI adding a class to the item of "shortcut". A follow up CL
will look at styling the icon with a shortcut badge if this class
exists.

Bug: b:279891186
Test: browser_tests --gtest_filter=*driveLinkToDirectory*
Change-Id: If40bae6e8b0df0d11f4d9f3348afc762cc30774e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4483918
Reviewed-by: Luciano Pacheco <lucmult@chromium.org>
Reviewed-by: Trent Apted <tapted@chromium.org>
Commit-Queue: Ben Reich <benreich@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1136996}