[CMAKE] Add a check-extended target

Summary:
This target is designed to run all the tests with the addition of the
"extended" ones. Currently equivalent to check-all with the extended
functional test suite.

Test Plan:

ninja check-extended

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D4882