feat(ssa_refactor)!: Add Slices

[vezenovm]

Description

Problem*

Resolves #582 and #1736

Works towards resolving issue #1556. This comment has more information on how we will add slices and Vectors into Noir: #1556 (comment).

Summary*

This PR adds syntax to enable slices (arrays without a known size during compilation). A slice's size is implicitly tracked during SSA and is represented as an array under the hood. Array syntax will remain the same but any types such as [Field] will be replaced by the new slices. Support is only included in the new SSA pass, thus some tech debt was included to conditionally handle slice vs. array compilation in the frontend.

Documentation

• This PR requires documentation updates when merged.

  • I will submit a noir-lang/docs PR.
  • I will request for and support Dev Rel's help in documenting this PR.

Additional Context

PR Checklist*

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

[jfecher]

Generally this looks very good. I do have some mostly frontend-related suggestions.

1. I see why we need this enable_slices flag. I was contemplating asking for a different syntax for slices until the new ssa becomes the default so that they can be separated from the previous deprecated slice syntax. I think now though we should just make an issue for removing enable_slices (or one for removing the old ssa ir and mention to remove enable_slices as well) and call it a day.
2. Can we remove Type::Vec as well? It is unused and we have different plans for implementing Vecs now so they won't need to be a primitive type anymore.

[jfecher]

👍

[jfecher]

👍