[backport#15886]Make SendConfirmationDialog fully fledged

Summary:
The property-based API has been used. Added support for the
informativeText and detailedText properties.

https://github.com/bitcoin/bitcoin/pull/15886/commits/654e419549fb5f1c360843d48e66eb098bbf5a83

Partial backport of Core PR15886

Test Plan:

ninja

run bitcoin-qt in regtest mode and check things out

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Subscribers: deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D7289