index: Implement lookup methods on block filter index.

Summary:
This is a partial backport of Core PR14121 : https://github.com/bitcoin/bitcoin/pull/14121/commits/b5e8200db76f06d35099da502439dcbdfd0a1b3e

Depends on D6338 and D6337

Test Plan:

ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D6339