[backport#14821] Replace CAffectedKeysVisitor with descriptor based logic

Summary:
0e75f44a0 Replace CAffectedKeysVisitor with descriptor based logic (Pieter Wuille)

Pull request description:

It seems we don't need a custom visitor pattern anymore to find what keys are affected by a script. Instead, infer the descriptor, and see which keys it expands to.

Backport of Core PR14821

Test Plan:

ninja check-all

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D6402