The in-memory block tree, mapping each block hash to its index entry.
Declared in <node/blockstorage.h>
[[guarded_by(0x7fbc8f17a878), guarded_by(0x7fbca3f03da8), guarded_by(0x7fbcace15ff8), guarded_by(0x7fbca6c57c68), guarded_by(0x7fbcad35f408), guarded_by(0x7fbc9fba11c8)]]
BlockMap m_block_index;