[backport#15986] Add unmodified-but-with-checksum to getdescriptorinfo

Summary:
https://github.com/bitcoin/bitcoin/pull/15986/commits/26d3fad1093dfc697048313be7a96c9adf723654

Depends on D6622

Concludes backport of Core PR15986

Test Plan:

ninja check
ninja
test_runner.py wallet_address_types

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D6623