[refactor] const ATMPArgs and non-const Workspace

Summary:
ATMPArgs should contain const arguments for validation.
The Workspace should contain state that may change
throughout validation.

This is a backport of core#21062 [3/4]
https://github.com/bitcoin/bitcoin/pull/21062/commits/174cb5330af4b09f3a66974d3bae783ea43b190e

Note: changes related to RBF are not applicable
Depends on D11779

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D11780