Make SigningProvider expose key origin information
Summary:
This is a partial backport of Core PR13723 : https://github.com/bitcoin/bitcoin/pull/13723/commits/84f1f1bfdf900cd28099e428441aa42f9d11a0ed
Depends on D4486
Test Plan:
make check ./test/functional/test_runner.py
Reviewers: #bitcoin_abc, jasonbcox
Reviewed By: #bitcoin_abc, jasonbcox
Differential Revision: https://reviews.bitcoinabc.org/D4489