Cache the immediate derivation parent xpub

Summary:
If unhardened derivation is used, cache the immediate derivation
parent xpub and use it for unhardened derivation

Backport of Core PR18204 part [5/7] : https://github.com/bitcoin/bitcoin/pull/18204/commits/f76733eda5f4c161e9eb47c74b949582ab8f448a

Depends on D8384 and D8385

Test Plan:

ninja all check

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Differential Revision: https://reviews.bitcoinabc.org/D8386