Load the descriptor cache from the wallet file

Summary:
Backport of Core PR16528 [15/43] : https://github.com/bitcoin/bitcoin/pull/16528/commits/2363e9fcaa41b68bf11153f591b95f2d41ff9a1a

Depends on D8408

Test Plan:

ninja all check-all

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Differential Revision: https://reviews.bitcoinabc.org/D8413