Warn on items more private than others

[asterite]

Problem

For example in this Rust code:

struct Foo {}

pub fn bar() -> Foo {
    Foo {}
}

Rust says that Foo is more private than bar.

We should do the same in Noir and also in similar cases (for example when defining a struct with fields that are more visible than the struct).

Happy Case

Noir warns/errors in the above snippet and similar ones.

Workaround

None

Workaround Description

No response

Additional Context

No response

Project Impact

None

Blocker Context

No response

Would you like to submit a PR for this Issue?

None

Support Needs

No response

[TomAFrench]

@asterite have you started on this? I'm thinking this could be a good issue for @aakoshh

[asterite]

No, I didn't start yet, so feel free to assign it to Akosh :-)

[aakoshh]

Tests can go into compiler/noirc_frontend/src/tests/visibility.rs
Look at Elaborator::elaborate_function for example