Add test for importing via descriptor

Summary:
This is a partial backport of Core PR14491 : https://github.com/bitcoin/bitcoin/pull/14491/commits/fbb5e935eaf17d603ec62e1a704a174235540b71

Depends on D6187 and D6191

Test Plan:

ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D6192