wallet: refactor GetNewDestination, use BResult

Summary:
Completes backport of core#25218: https://github.com/bitcoin/bitcoin/pull/25218/commits/111ea3ab711414236f8678566a7884d48619b2d8

Partial backport of core#25721.

Depends on D17956.

Test Plan:

ninja all check-all

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D17957