nightly-2024-03-14: chore: Add `Instruction::DecrementRc` (#4525)

# Description

## Problem\*

Resolves https://github.com/noir-lang/noir/issues/4522

## Summary\*

Experimenting with this to see how much it improves performance of
unconstrained code using arrays.

## Additional Context

Currently the new dec_rc instruction is only issued for function
parameters when a function is finished - assuming the parameters are not
also returned.

CC @sirasistant for visibility

## Documentation\*

Check one:
- [x] No documentation needed.
- [ ] Documentation included in this PR.
- [ ] **[Exceptional Case]** 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.

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Co-authored-by: Álvaro Rodríguez <[email protected]>