If unhardened derivation is used, cache the immediate derivation
parent xpub and use it for unhardened derivation
Backport of Core [[https://github.com/bitcoin/bitcoin/pull/18204 | PR18204]] part [5/7] : https://github.com/bitcoin/bitcoin/pull/18204/commits/f76733eda5f4c161e9eb47c74b949582ab8f448a
Depends on D8384 and D8385