Improve Indices on pruned nodes via prune blockers

Summary:
Completes backport of core#21726:
https://github.com/bitcoin/bitcoin/pull/21726/commits/825d19839bf71245306d4c8edde040e5941caa46
https://github.com/bitcoin/bitcoin/pull/21726/commits/de08932efa953e9a237cbf879460488ad8947411
https://github.com/bitcoin/bitcoin/pull/21726/commits/71c3f0356c01521a95c64fba1e7375aea6286bb0

Depends on D17389.

Backport of core#25123.

Test Plan:

./test/functional/test_runner.py feature_index_prune

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D17390