[refactor] comment/naming improvements

Summary:
This backports the rest of the changes that are not already squashed with other commits in the core#20833 stack. The reason they were not included with other commits is that the relevant code was already landed before I noticed this follow-up (D12101)

This is a partial backport of core#22084
https://github.com/bitcoin/bitcoin/pull/22084/commits/e8ecc621be6afd3252c0f8147e42c3b4918f7f46

Depends on D12133

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D12134