Implement createTerminatedStateAccount internal function

[mitsuaki-u]

Description

Add function below to interoperability store:

createTerminatedStateAccount(chainID, stateRoot = None):
    if stateRoot:
        if chainAccount(chainID) exists:
            chainAccount(chainID).status = CHAIN_TERMINATED
            remove the entry with storeKey = uint32be(chainID) from the outbox root substore

        terminatedState = {
            "stateRoot": stateRoot, 
            "mainchainStateRoot": EMPTY_BYTES,
            "initialized": True
        }

    elif chainAccount(chainID) exists:
        chainAccount(chainID).status = CHAIN_TERMINATED
        remove the entry with storeKey = uint32be(chainID) from the outbox root substore

        terminatedState = {
            "stateRoot": chainAccount(chainID).lastCertificate.stateRoot, 
            "mainchainStateRoot": EMPTY_BYTES,
            "initialized": True
        }
    # State root is not available, set it to empty bytes temporarily. 
    # This should only happen on a sidechain.
    else:
        # Processing on the mainchain
        if ownChainAccount.ID == MAINCHAIN_ID:
            # If the account does not exist on the mainchain, the input chainID is invalid.
            return False

        terminatedState = {
            "stateRoot": EMPTY_BYTES,
            "mainchainStateRoot": chainAccount(MAINCHAIN_ID).lastCertificate.stateRoot, 
            "initialized": False
        }

    create an entry in the terminated state substore with 
        storeKey = uint32be(chainID) 
        storeValue = serialization of terminatedState

    return True

Acceptance Criteria

• Add unit tests for all function paths