[wallet] Add change type to CCoinControl
This is extracted from Core PR12194 . The rest of the PR is not interesting for us at this stage, but this part will avoid merge conflicts.
Depends on D3661
Reviewers: #bitcoin_abc, jasonbcox
Reviewed By: #bitcoin_abc, jasonbcox
Differential Revision: https://reviews.bitcoinabc.org/D3662