DefaultMetadataLoader was changed to private, making it difficult to print out metadata

Hi,

A recent commit bdacdfe made the DefaultMetadataLoader struct private to the crate.
This makes it impossible to print out the crate metadata using the given functions unless I define my own struct which implements the MetadataLoader trait. I'm currently just trying to understand the metadata file better, and am working with an older version of the Rust compiler so that I can access this type. I'm wondering why this type was made private.

Here is the code I'm using which works with an older version of the compiler:

fn main() {
    let path = std::env::args().nth(1).expect("no path given");
    let path = Path::new(&path);
    let triple = TargetTriple::from_triple("x86_64-apple-darwin");
    let target = Target::expect_builtin(&triple);
    let mut stdout = io::stdout();

    rustc_span::create_session_globals_then(Edition::Edition2018, || {
        let _ = locator::list_file_metadata(&target, path, &DefaultMetadataLoader, &mut stdout);
    });
}

Start by reviewing commit bdacdfe and the visibility of DefaultMetadataLoader alongside the MetadataLoader trait and locator::list_file_metadata. Trace how metadata printing is intended to work and check the surrounding compiler tests or API guidance. Done means the supported way to print crate metadata is clear and the visibility or usage path is addressed consistently.