coins: pass linked list of flagged entries to BatchWrite

Summary:
BatchWrite now iterates through the linked
list of flagged entries instead of the entire
coinsCache map.

Co-Authored-By: l0rinc <pap.lorinc@gmail.com>

This is a partial backport of core#28280
https://github.com/bitcoin/bitcoin/pull/28280/commits/7825b8b9aeceb4ff607650cdc9c49e5de9c7719f

Depends on D18617

Test Plan: ninja all check-all bitcoin-fuzzers

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D18618