Implement state-sync process #3046
Description
Currently, we have active-sync that catches a node up to the latest block in the chain, and passive-sync that gradually downloads blocks, transactions, and receipts going backwards towards genesis.
In the case of passive-sync it does not download the state. So, while there is useful information about the block, the state at that point in time is not available in the database.
The new state-sync feature will attempt to remedy this by utilising an older checkpoint file. It will restore the state_trie from the checkpoint file and then replay the blocks going forwards. Since the blocks, transactions and receipts already exist in the database, the purpose is simply to recreate the missing nodes of the state_trie at a historical point in time.