LookupBlockIndex -> CACHED_INVALID

Summary:
Co-authored-by: Anthony Towns <aj@erisian.com.au>

This is a partial backport of Core PR15141 : https://github.com/bitcoin/bitcoin/pull/15141/commits/7df16e70e67c753c871797ce947ea09d7cb0e519

Depends on D6698

Test Plan:

ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D6700