c9e6e7ed7 wallet: add cachable amounts for caching credit/debit values (Karl-Johan Alm)
Pull request description:
This is a refactoring that will make #13756 a lot cleaner and straight-forward, since it adds another combination to the pile (watch-only * spendable * reused).
It's also a nice change in general.
Tree-SHA512: 6c876d58bbffd5cb85ef632dea4fd6afed163904bbde5efdb307fa119af178ed3cb5df047255da7e9a9136fed876922f1116fce61a3710f308c72275f9b7d18b