Function compute_state_hash 

pub fn compute_state_hash(
    group_id: &str,
    revision: u64,
    prev_state_hash: Option<&str>,
    roster_root: &str,
    policy_hash: &str,
    public_meta_hash: &str,
    security_binding: Option<&str>,
    withdrawn: bool,
) -> String

Compose the final state_hash from its parts.