The in-memory block tree, mapping each block hash to its index entry.
Declared in <node/blockstorage.h>
[[guarded_by(0x7f2e1b098a98), guarded_by(0x7f2e26d1a1f8), guarded_by(0x7f2e375e02d8), guarded_by(0x7f2e33367698), guarded_by(0x7f2e3542e688), guarded_by(0x7f2e28a731e8)]]
BlockMap m_block_index;