wallet: Change output type globals to members

Summary:
This is a backport of Core PR12408

Depends on D3663, D3664 and D3662

Test Plan:

make check
test/functional/test_runner.py

Reviewers: #bitcoin_abc, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Differential Revision: https://reviews.bitcoinabc.org/D3665