UNO-Desktop: Deduplicate bookmarks for new sign-in users on initial sync

When a user turns off sync and chooses to keep their data, their local
bookmarks are initially an exact match of the server bookmarks. If the
user signs back in with account bookmark storage enabled, they will have
separate storage for account and local bookmarks. The account storage
downloads the bookmarks from the server, while the local storage remains
as is. This can result in many duplicate bookmarks.

This CL introduces a deduplication logic that is triggered during the
initial sync. The `InitialAccountBookmarkDeduplicator` class removes
bookmarks from local storage; account bookmarks are never modified. The
deduplicator only removes direct children (and their descendants, if
any) of the permanent nodes. A local direct child is removed if and only
if it matches an account child of the same account permanent parent, and
the tree rooted at the local child is a subgraph of the tree rooted at
the account child.

Fixed: 417948376
Change-Id: Idcd929c8f63eee8d70f0faf9828bd8169c21d977
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6964960
Commit-Queue: Mahmoud Rashad <mmrashad@google.com>
Reviewed-by: Mikel Astiz <mastiz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1519671}