Now BlockManager::LoadBlockIndex() will ACTUALLY only load BlockMan
members.
[META] In a later commit, pindexBestHeader will be moved to ChainMan as a member
-----
Code Reviewer Notes
Call graph of relevant functions:
`ChainstateManager::LoadBlockIndex()`<-- Moved to
calls `BlockManager::LoadBlockIndexDB()`
which calls `BlockManager::LoadBlockIndex()` <-- Moved from
There is only one call to each of inner functions, meaning that no
behavior is changing.
This is a partial backport of [[https://github.com/bitcoin/bitcoin/pull/24909 | core#24909]]
https://github.com/bitcoin/bitcoin/pull/24909/commits/5d670173a32ccdcb25d3a6bf97317f0ac774e0ed