Harness: Dedupe accounts and coalesce privileges

[buffalojoec]

Problem

Currently, if you provide the same account twice to Mollusk's process_instruction API, the permissions are taken directly from the instruction AccountMeta entries, so even if two metas have the same public key, their perms as AccountInfo will reflect those of the instruction metas.

In other words, if I provide the same account twice, as so...

let key = Pubkey::new_unique();
let metas = vec![
    AccountMeta::new(key, false),         // writable
    AccountMeta::new_readonly(key, true), // signer
];

... then my program will see the first account as writable, and the second as a signer, but they will have the same address. These must be coalesced, as is done in the VM's serialization step. Unfortunately, this deduping depends on the TransactionContext, so this fix has to go into Mollusk!

Summary of Changes

Employ a simple map and an extra iteration to coalesce account privileges across accounts with the same address.