Migrate brave sync to USS bookmarks

[darkdh]

https://www.chromium.org/developers/design-documents/sync/unified-sync-and-storage-overview

https://chromium.googlesource.com/chromium/src/+/8554331912828c09f8a26a33ddd52d7838f722b0
is landed in C78 which causes our bookmarks sync doesn't work
(#6435 which will be addressed by workaround adding kSyncUSSBookmarks to disable feature list in BraveMainDelegate)

We have to prepare for the case before BookmarkChangeProcessor and BookmarkModelAssociator and other related things will be completely deprecated

[darkdh]

According to https://bugs.chromium.org/p/chromium/issues/detail?id=933756
They will be removed in 80.0.3947.0

[btlechowski]

Verification passed on

Brave	1.3.110 Chromium: 80.0.3987.78 (Official Build) (64-bit)
Revision	cb5aa81cb0a3a2c674b93bc7ffb34a86cd3b4802-refs/branch-heads/3987@{#752}
OS	Ubuntu 18.04 LTS

Verified test plan from brave/brave-core#4324 (comment)
Also test by switching the devices.

[Pass] Add (1)
[Pass] Add with existing bookmarks (2)
[Pass] Add with same order (3)
[Pass] Move
[Pass] Modify
[Pass] Reorder (1)
[Pass] Reorder (2)
[Pass] Delete
[Pass] Migration/Upgrade - Verified Move, Delete, Modify, Reorder(1), Reorder(2)

Verification passed with

Brave	1.3.111 Chromium: 80.0.3987.85 (Official Build) (64-bit)
Revision	583b05dfa4ffc657f0f7c5cc13f53aa17c9a5bcf-refs/branch-heads/3987@{#791}
OS	macOS Version 10.14.6 (Build 18G103)

Verified test plan from brave/brave-core#4324 (comment)

[Pass] Add (1)
[Pass] Add with existing bookmarks (2)
[Pass] Add with same order (3)
[Pass] Move
[Pass] Modify
[Pass] Reorder (1)
[Pass] Reorder (2)
[Pass] Delete
[Pass] Migration/Upgrade - Verified Move, Modify, Reorder(1), Reorder(2), Delete

Verification passed on

Brave	1.3.112 Chromium: 80.0.3987.87 (Official Build) (64-bit)
Revision	449cb163497b70dbf98d389f54e38e85d4c59b43-refs/branch-heads/3987@{#801}
OS	Windows 10 OS Version 1803 (Build 17134.1006)

[Pass] Add (1)
[Pass] Add with existing bookmarks (2)
[Pass] Add with same order (3)
[Pass] Move
[Pass] Modify
[Pass] Reorder (1)
[Pass] Reorder (2)
[Pass] Delete
[Pass] Migration/Upgrade - Verified Move, Modify, Reorder(1), Reorder(2), Delete