c9017ce3bc protect g_chainman with cs_main (James O'Beirne)
2b081c4568 test: add basic tests for ChainstateManager (James O'Beirne)
4ae29f5f0c use ChainstateManager to initialize chainstate (James O'Beirne)
5b690f0aae refactor: move RewindBlockIndex to CChainState (James O'Beirne)
89cdf4d569 validation: introduce unused ChainstateManager (James O'Beirne)
8e2ecfe249 validation: add CChainState.m_from_snapshot_blockhash (James O'Beirne)
Pull request description:
This is part of the [assumeutxo project](https://github.com/bitcoin/bitcoin/projects/11):
Parent PR: #15606
Issue: #15605
Specification: https://github.com/jamesob/assumeutxo-docs/tree/master/proposal
---
This changeset introduces `ChainstateManager`, which is responsible for creating and managing access to multiple chainstates. Until we allow chainstate creation from UTXO snapshots (next assumeutxo PR?) it's basically unnecessary, but it is a prerequisite for background IBD support.
Changes are also made to the initialization process to make use of `g_chainman` and thus clear the way for multiple chainstates being loaded on startup.
One immediate benefit of this change is that we no longer have the `g_blockman` global, but instead have the ChainstateManager inject a reference of its shared BlockManager into any chainstate it creates.
Another immediate benefit is that uses of `ChainActive()` and `ChainstateActive()` are now covered by lock annotations. Because use of `g_chainman` is annotated to require cs_main, these two functions subsequently follow.
Because of whitespace changes, this diff looks bigger than it is. E.g., 4813167d98 is most easily reviewed with
```sh
git show --color-moved=dimmed_zebra -w 4813167d98
```
ACKs for top commit:
MarcoFalke:
re-ACK c9017ce3bc📙
fjahr:
Code Review Re-ACK c9017ce3bc
ariard:
Code Review ACK c9017ce
ryanofsky:
Code review ACK c9017ce3bc. No changes since last review other than a straight rebase
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10358a381a