[backport#17304 13/18] Refactor: Move Upgrade code out of CWallet::CreateWalletFromFile

Summary:
This commit does not change behavior.

https://github.com/bitcoin/bitcoin/pull/17304/commits/8b0d82bb428de9e7f1da7c61574e7a8376a62d43

Depends on D7159

Partial backport of Core PR17304

Test Plan:

ninja check

Reviewers: #bitcoin_abc, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Differential Revision: https://reviews.bitcoinabc.org/D7160