test: Unit test for block filter index reorg handling.

Summary:
This is a partial backport of Core PR14121 : https://github.com/bitcoin/bitcoin/pull/14121/commits/2bc90e4e7bf7fef56830b33b1fba678fd0dbd6d8

Depends on D6340

Test Plan:

ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D6341