Merge #10165: [Wallet] Refactoring by using CInputCoin instead of std::pair

Summary:
Backport of Core PR10165
https://github.com/bitcoin/bitcoin/pull/10165/files

Completes T523

Co-authored-by: Jason B. Cox <contact@jasonbcox.com>

Test Plan:
ninja check
make check
bitcoin-qt loads and can send transactions as expected

Reviewers: deadalnix, Fabien, #bitcoin_abc

Reviewed By: Fabien, #bitcoin_abc

Subscribers: teamcity, schancel

Differential Revision: https://reviews.bitcoinabc.org/D2335