Update Sync ownership in components/autofill

components/autofill/core/browser/webdata/OWNERS used to give the sync
team co-ownership of some sync-related files (bridges and model type
controllers) in autofill, using per-file entries.
However, the relevant source files have since been moved into
subfolders, so the per-file entries didn't apply anymore.
This CL creates new OWNERS files in the relevant subdirectories.
It also slightly expands sync's ownership from "*sync_bridge*" to
"*sync*" - this also includes "sync_util" files now, mostly containing
helpers to convert between sync and autofill types.

Bug: none
Change-Id: Id3d9bb917f71b4728457fc8a7ec86e26a3741045
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5300594
Reviewed-by: Florian Leimgruber <fleimgruber@google.com>
Commit-Queue: Marc Treib <treib@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1261538}