[backport#17304 15/18] Refactor: Move SetupGeneration code out of CWallet

Summary:
This commit does not change behavior.

https://github.com/bitcoin/bitcoin/pull/17304/commits/0eac7088ab878372a72f85f9c5f7662a14199083

Depends on D7161

Partial backport of Core PR17304

Test Plan:

ninja check

Reviewers: #bitcoin_abc, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Subscribers: jasonbcox

Differential Revision: https://reviews.bitcoinabc.org/D7162