[ios] Move AuthenticationService{,Factory} to their own targets

This is the last step to break the circular dependency between
AuthenticationService and BrowsingDataRemover (after this it
will be possible to use BrowsingDataRemover directly from the
AuthenticationServiceFactory).

This is part of a multi-CLs change:
  - https://crrev.com/c/5961720
  - https://crrev.com/i/7766952
  - https://crrev.com/c/5961581
  - https://crrev.com/c/5961504
  - https://crrev.com/c/5961143
  - https://crrev.com/i/7775666
  - https://crrev.com/c/5962001
  - https://crrev.com/c/5961341
  - https://crrev.com/c/5961505
  - https://crrev.com/c/5961144
  - https://crrev.com/c/5961743
 => https://crrev.com/c/5961506

Bug: 325612973
Change-Id: If26df7c853d295c6ba1dc527736714b424692f11
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5961506
Commit-Queue: Sylvain Defresne <sdefresne@chromium.org>
Reviewed-by: Boris Sazonov <bsazonov@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1374833}