Extract the compact block processing into a generic helper class

Summary:
This moves the logic out of the compact block into a new ShortIdProcessor that can be reused for the compact proofs. This also makes the code a bit easier to follow.

Depends on D11569.

Test Plan:

ninja all check-all

Reviewers: #bitcoin_abc, sdulfari

Reviewed By: #bitcoin_abc, sdulfari

Subscribers: sdulfari, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D11571