Allow CRX-internal symlinks on macOS

Allow the updater to preserve internal symbolic links when extracting
CRX files on macOS. This is necessary for supporting "zip" installers
for the Updater and Chrome, which include an internal link to ksadmin.

This is implemented as an option on update-client's in-process unzipper
which is only enabled for //chrome/updater. There shouldn't be a reason
to enable it for webview's component updater.

Fixed: 411228564
Change-Id: I5455d28a8007cb139cbf741db0f8ca6a12427c33
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6496428
Reviewed-by: Peter Pakkenberg <pbirk@chromium.org>
Reviewed-by: Joshua Pawlicki <waffles@chromium.org>
Auto-Submit: Noah Rose Ledesma <noahrose@google.com>
Commit-Queue: Noah Rose Ledesma <noahrose@google.com>
Cr-Commit-Position: refs/heads/main@{#1453908}