log: Log VerifyDB Progress over multiple lines

Summary:
This allows to log a timestamp for each entry, and avoids potential interference with other threads that could log concurrently.

This concludes backport of core#27009
https://github.com/bitcoin/bitcoin/pull/27009/commits/fe683f352480245add0b27fe7efef5fef4c1e8c3

Depends on D14921

Test Plan:
ninja && src/bitcoind

src/bitcoin-cli verifychain 4 10000

Check the output of the bitcoind process.

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D14922