feat(acir)!: Add a public outputs field

[kevaundray]

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• I have tested the changes locally.
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[TomAFrench]

Now we have an explicit return type on the ABI this should be able to be handled seamlessly by the evaluator. Would you like me to fix up any conflicts so we can get this merged?

[kevaundray]

Just merged the conflicts -- One thing to double check is that the definition of public outputs here also matches the definition being used in Noir

[TomAFrench]

Based on https://aztecprotocol.slack.com/archives/C0183F0V42V/p1676636370362909?thread_ts=1676636143.866669&cid=C0183F0V42V, we may want to take the opportunity to rename these fields for more clarity.

[kevaundray]

LGTM - one small comment re docs

[kevaundray]

This LGTM -- @TomAFrench you'll need to approve since the PR was originally made by me

[TomAFrench]

Ah, that's true. Thanks. Approving now.