Add support for nested arrays on unconstrained functions

[sirasistant]

Problem

Now that AOS2SOA has been removed, we need to support nested arrays in brillig to support arrays of structs that hold arrays inside them.

Happy Case

The following should compile:

struct Header {
    params: [Field; 3],
}

struct MyNote {
    plain: Field,
    array: [Field; 2],
    header: Header,
}

unconstrained fn access_nested(notes: [MyNote; 2], x: Field, y: Field) -> Field {
    notes[x].array[y] + notes[y].array[x] + notes[x].plain + notes[y].header.params[x]
}

unconstrained fn create_inside_brillig(x: Field, y: Field) {
    let header = Header { params: [1, 2, 3]};
    let note0 = MyNote { array: [1, 2], plain : 3, header };
    let note1 = MyNote { array: [4, 5], plain : 6, header };
    assert(access_nested([note0, note1], x, y) == (2 + 4 + 3 + 1));
}

fn main(x: Field, y: Field) {
    let header = Header { params: [1, 2, 3]};
    let note0 = MyNote { array: [1, 2], plain : 3, header };
    let note1 = MyNote { array: [4, 5], plain : 6, header };

    create_inside_brillig(x, y);
    assert(access_nested([note0, note1], x, y) == (2 + 4 + 3 + 1));
}

Alternatives Considered

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Additional Context

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Would you like to submit a PR for this Issue?

Yes

Support Needs

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