feat: allow printing each SSA interpreter definition

[asterite]

Description

Problem

No issue, but something I already used a couple of times to debug issues with the SSA interpreter or with SSA in general.

Summary

This PR adds a --print-definitions flag to nargo interpret. When passed, each definition in the SSA interpret will be shown to console. This is most useful when combined with --show-ssa. For example for this code:

// x = 1, y = 2
fn main(x: Field, y: Field) {
    let _ = x + y;
}

Running nargo interpret --show-ssa --print-definitions we get:

After Initial SSA:
acir(inline) fn main f0 {
  b0(v0: Field, v1: Field):
    v2 = add v0, v1
    return
}

v0 = Field 1
v1 = Field 2
v2 = Field 3
--- Interpreter result after Initial SSA:
Ok([])

(snip)

Additional Context

Documentation

Check one:

• No documentation needed.
• Documentation included in this PR.
• [For Experimental Features] Documentation to be submitted in a separate PR.

PR Checklist

• I have tested the changes locally.
• I have formatted the changes with Prettier and/or cargo fmt on default settings.

[jfecher]

Neat!