feat(nargo)!: save program ABI alongside ACIR

[TomAFrench]

Related issue(s)

Resolves #897

Description

Summary of changes

Rather than serializing a Circuit into a acir file, we now serialize a CompiledProgram (Circuit + Abi) into a json file.

We still make use of the custom serialisation method for Circuit however JSON doesn't store bytes directly so we end up with an array. We could fix this by just encoding the entire thing into bytes rather than using json atm (and allowing exporting a JSON ABI separately).

An example output (for the simple_shield circuit) is shown below:

{
  "circuit": [0, 0, 0, 0, 21, 0, 0, 0, 3, 0, 0, 0, 2, 0, 0, 0, 13,  /*snip*/ ],
  "abi": {
    "parameters": [
      {
        "name": "priv_key",
        "type": {
          "kind": "field"
        },
        "visibility": "private"
      },
      {
        "name": "note_root",
        "type": {
          "kind": "field"
        },
        "visibility": "public"
      },
      {
        "name": "index",
        "type": {
          "kind": "field"
        },
        "visibility": "private"
      },
      {
        "name": "note_hash_path",
        "type": {
          "kind": "array",
          "length": 3,
          "type": {
            "kind": "field"
          }
        },
        "visibility": "private"
      },
      {
        "name": "to_pubkey_x",
        "type": {
          "kind": "field"
        },
        "visibility": "private"
      },
      {
        "name": "to_pubkey_y",
        "type": {
          "kind": "field"
        },
        "visibility": "private"
      }
    ],
    "param_witnesses": {
      "index": [
        3
      ],
      "note_hash_path": [
        4,
        5,
        6
      ],
      "note_root": [
        2
      ],
      "priv_key": [
        1
      ],
      "to_pubkey_x": [
        7
      ],
      "to_pubkey_y": [
        8
      ]
    },
    "return_type": {
      "kind": "array",
      "length": 2,
      "type": {
        "kind": "field"
      }
    },
    "return_witnesses": [
      13,
      15
    ]
  }
}

Dependency additions / changes

Test additions / changes

Checklist

• I have tested the changes locally.
• I have formatted the changes with Prettier and/or cargo fmt with default settings.
• I have linked this PR to the issue(s) that it resolves.
• I have reviewed the changes on GitHub, line by line.
• I have ensured all changes are covered in the description.
• This PR requires documentation updates when merged.

Additional context

[kevaundray]

LGTM