Merge #12639: Reduce cs_main lock and avoid extra lookups of mapAddressBook in listunspent RPC

Summary:
Reduce cs_main lock in listunspent and refactor replacing three mapAddressBook lookups with one.

Backport of Core PR12639
https://github.com/bitcoin/bitcoin/pull/12639/

Test Plan:

../configure --enable-debug
make check
test_runner.py

Reviewers: deadalnix, Fabien, jasonbcox, O1 Bitcoin ABC, #bitcoin_abc

Reviewed By: deadalnix, O1 Bitcoin ABC, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D4516