nightly-2024-04-23: feat(acir_gen): Brillig stdlib (#4848)

# Description

## Problem\*

Expands usage of https://github.com/noir-lang/noir/issues/3907 to our
Brillig directives.

## Summary\*

The Brillig stdlib differs slightly from normal Brillig functions calls.
We can insert the generated Brillig bytecode at any point during ACIR
gen. This includes within the `GeneratedAcir` struct itself. We have a
few requirements on what we want to achieve:
- We do want to have to thread the ACIR gen `SharedContext` that is used
for generating normal Brillig function pointers to the `GeneratedAcir`.
Why would we want a reference to code generation inside of our Generated
ACIR structure (we don't)?
- We want to maintain one Brillig stdlib for an entire program. We do
not want to change the `BrilligCall` opcode so we need them to be a part
of the main list of `unconstrained_functions` in a program.
- Function IDs reference a flat list, so reserving some number of slots
would be wasteful if the program does not eventually use a Brillig
stdlib function in that slot.

So instead we maintain a map as part of the `GeneratedAcir` that notes
when we at which opcode location we inserted a call to a
`BrilligStdlibFunc`. The ID at this point will just be `0`. After
finishing ACIR generation for a function, only then do we resolve the
IDs for these `BrilligCall` opcodes.

## Additional Context



## Documentation\*

Check one:
- [X] No documentation needed.
- [ ] Documentation included in this PR.
- [ ] **[For Experimental Features]** Documentation to be submitted in a
separate PR.

# PR Checklist\*

- [X] I have tested the changes locally.
- [X] I have formatted the changes with [Prettier](https://prettier.io/)
and/or `cargo fmt` on default settings.

---------

Co-authored-by: Tom French <[email protected]>
Co-authored-by: jfecher <[email protected]>
Co-authored-by: TomAFrench <[email protected]>