Macro v2 can see private items, but we don't name resolve it

Rustc accepts this code, but we don't:

#![feature(decl_macro)]

mod privacy_boundary {
    mod inner {
        pub fn x() -> i32 {
            5
        }
    }

    pub macro m() {
        $crate::privacy_boundary::inner::x()
    }
}

use privacy_boundary::m;

fn main() {
    let v = m!(); // we report the type of v as {unknown}
    dbg!(v);
}

Somehow unrelated: maybe we should resolve names even if they are private?

Start with the supplied Rust reproducer and compare rust-analyzer's result with rustc's accepted behavior; no file or test is named. Trace macro v2 name resolution across the privacy boundary, and consider the issue complete when the example resolves v as i32 instead of {unknown}, with the behavior covered by a test.