feat: visibility for modules

[asterite]

Description

Problem

Part of #4515

Summary

Additional Context

I made most of the stdlib modules public. These are all except the test modules and some modules that I thought were just implementation details of some other modules.

I'm adding very short documentation for each of these. I'm thinking that once we get all visibility done it should be documented in its own section, with examples.

Documentation

Check one:

• No documentation needed.
• Documentation included in this PR.
• [For Experimental Features] Documentation to be submitted in a separate PR.

PR Checklist

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

[github-actions]

🚀 Deployed on https://66f6e766a744c2a7b593647f--noir-docs.netlify.app

[TomAFrench]

fn main(x: Field) {
    let y = foo::bar::baz();
    assert_eq(x, y);
}

mod foo {
    mod bar {
        pub fn baz() -> Field {
            2
        }
    }
}

This program currently throws two warnings rather than one.

warning: bar is private and not visible from the current module
  ┌─ temp/src/main.nr:2:18
  │
2 │     let y = foo::bar::baz();
  │                  --- bar is private
  │

warning: bar is private and not visible from the current module
  ┌─ temp/src/main.nr:2:18
  │
2 │     let y = foo::bar::baz();
  │                  --- bar is private
  │

[TomAFrench]

Looks good, we should add a bunch of frontend tests for this to show that behaviour matches that of rust

[asterite]

@TomAFrench it seems that duplicate error also happens with private functions... which means that this error already existed a long time before this PR. Do you think I should try to fix it in this PR?

[asterite]

If I remember correctly two path lookups are done, one to check if it's a trait-method call, and the two lookups end up triggering duplicate errors. I'd prefer to fix it in a separate PR (maybe cleaner). But let me know.

[TomAFrench]

If it's a preexisting error then there's no reason to block this PR over it. We can sort it in a separate PR.

[asterite]

Looks good, we should add a bunch of frontend tests for this to show that behaviour matches that of rust

Do you know what things we could test? To be honest I don't know all the details of Rust's visibility... but if module visibility behaves the same as functions, structs, etc., then it probably works fine as the visibility check is the same for any item.

[TomAFrench]

I'd just want to test that you can't reach through private modules to access public contents (except for direct submodules). That's the main case I'd want to test (how I noticed that we threw multiple warnings)

[TomAFrench]

Nico's monday is gonna be ruined but LGTM

[github-actions]

FYI @noir-lang/developerrelations on Noir doc changes.