[backport#16227 1/8]Add HaveKey and HaveCScript to SigningProvider

Summary:
https://github.com/bitcoin/bitcoin/pull/16227/commits/1b699a5083b435c2b79f3951f94ac9f967d24f6c

Partial backport of Core PR16227

Test Plan:

ninja check

Reviewers: #bitcoin_abc, deadalnix, nakihito

Reviewed By: #bitcoin_abc, deadalnix, nakihito

Differential Revision: https://reviews.bitcoinabc.org/D6553