Warn/error if using struct constructor and there's at least one private field

[asterite]

Problem

Once #6221 is merged, this code:

mod moo {
    pub struct Foo {
        x: Field
    }
}

fn main() {
    let _ = moo::Foo { x: 1 };
}

errors saying that x is private. However, a better error message could be that Foo can't be constructed (outside of its module) because some of its fields are private.

Happy Case

The compiler gives a clearer error message.

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?

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Support Needs

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