feat!: ACVM no longer takes ownership over opcodes

[TomAFrench]

Description

Problem*

Resolves

Summary*

With the changes in #399, the only reason that ACVM needs ownership over the circuit's opcodes is that it needs to be able to write the return values from foreign calls into the Brillig opcodes. This doesn't really make sense as this is ACVM state rather than a property of the bytecode.

I've then moved these into a hashmap held on the ACVM struct which get injected into the solver when we encounter a brillig opcode.

Additional Context

PR Checklist*

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