Functional tests for descriptor wallets

Summary:
Backport of Core PR16528 [37/43] : https://github.com/bitcoin/bitcoin/pull/16528/commits/1346e14831489f9c8f53a08f9dfed61d55d53c6f

Depends on D8475

Test Plan:

ninja all check-all

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Subscribers: majcosta

Differential Revision: https://reviews.bitcoinabc.org/D8487