Give ZMQ consistent order with UpdatedBlockTip on scheduler thread

Summary:
Note that UpdatedBlockTip is also used in net_processing to
announce new blocks to peers. As this may need additional review,
this change is included in its own commit.

This is a partial backport of Core PR10286 : https://github.com/bitcoin/bitcoin/pull/10286/commits/3ea8b75281edc60078423bd5d277cd2a84aa5d33

Test Plan:

make check
./test/functional/test_runner.py interface_zmq.py

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D3154