Add recursion into acir format

[kevaundray]

Problem

Once acvm adds the recursion opcode it will need to be supported by the backend.

Solution

We add a recursion field to the acir_format and implement the code to handle it.

This task should be considered complete when we add the relevant code to process a recursion opcode and when we add a test in the test folder to ensure that this works on the cpp side.

[zac-williamson]

Working on this in zw/noir-recursion

Currently I'm implementing recursion where the requirement is the circuit has a single public input. Is this too strict? (if multiple inputs are required, the outer circuit hashes them together).

Doing this makes the UltraPlonk proof data constant-sized, which could help.

I have implemented a Recursion type into acir_format with some passing tests, one missing thing is serialisation functions that will be needed by barretenberg_sys to turn inner proofs/verification keys into a format that is required by the Recursion constraint.

[Savio-Sou]

Closed with #485.