Convert wallet to new serialization

Summary:
This is a backport of Core PR19032 [2/4]
https://github.com/bitcoin/bitcoin/pull/19032/commits/ef17c03e074b6c3f185afa4eff572ba687c2a171

Depends on D9244

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D9245