[Sync] Move some directory-related things from core/ to syncable/.
Everything is being moved out of core to better homes. Things moved:
syncable/
base_node
base_transaction
change_record
change_reorder_buffer
delete_journal
read_node
read_transaction
test_user_share
user_share
write_node
write_transaction
My knowledge of the role each of these plays is not perfect, so let me
know if something should not have been moved.
BUG=631271
Review-Url: https://codereview.chromium.org/2407163004
Cr-Commit-Position: refs/heads/master@{#424743}
60 files changed