[backport#15780] wallet: add cachable amounts for caching credit/debit values

Summary:
https://github.com/bitcoin/bitcoin/pull/15780/commits/c9e6e7ed79886b702614e627a966fc9a4850f8f0

Backport of Core PR15780

Test Plan:

ninja check-all

Reviewers: #bitcoin_abc, nakihito

Reviewed By: nakihito

Differential Revision: https://reviews.bitcoinabc.org/D6347