`RewindBlockIndex` was made to allow nodes upgrading to new consensus rules post-segwit fork to 
download new consensus data (i.e witnesses) without having to go through a whole IBD. It has been pointed than now really few pre-segwit nodes care to upgrade and that this logic may be irrelevant.

See https://github.com/bitcoin/bitcoin/pull/17737#discussion_r358514335 in review  of #17737 for more context pointers.
* Mutable because we need to be able to mark IsInitialBlockDownload()
     * const, which latches this for caching purposes.
     */
    mutable std::atomic<bool> m_cached_finished_ibd{false};
    
    CTxMemPool& m_mempool;
    
    std::unique_ptr<CoinsViews> m_coins_views;
public:
    
    
    BlockManager& m_blockman;
    explicit CChainState(CTxMemPool& mempool, BlockManager& blockman, uint256 from_snapshot_blockhash = uint256());
    /**
     * Initialize the CoinsViews UTXO set database management data structures. The in-memory
     * cache is initialized separately.
     *
     * All parameters forwarded to CoinsViews.
     */
    void InitCoinsDB(
        size_t cache_size_bytes,
        bool in_memory,
        bool should_wipe,
        std::string leveldb_name = "chainstate");
    
    
    void InitCoinsCache(size_t cache_size_bytes) EXCLUSIVE_LOCKS_REQUIRED(::cs_main);
    
    
    bool CanFlushToDisk() const EXCLUSIVE_LOCKS_REQUIRED(cs_main) {