Generalize PublicOnlySigningProvider into HidingSigningProvider

Summary:
This is a partial backport of Core PR13723 : https://github.com/bitcoin/bitcoin/pull/13723/commits/81e1dd5ce1a32114a38691ec6b55e72ab04dbbb1

Depends on D4489

Test Plan:

make check
./test/functional/test_runner.py

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D4490