Generate new descriptors when encrypting
Summary:
Backport of Core PR16528 [34/43] : https://github.com/bitcoin/bitcoin/pull/16528/commits/1cb42b22b11c27e64462afc25a94b2fc50bfa113
Depends on D8455
Test Plan:
ninja all check-all
Reviewers: #bitcoin_abc, Fabien
Reviewed By: #bitcoin_abc, Fabien
Differential Revision: https://reviews.bitcoinabc.org/D8457