Add std::os::unix::fs::DirEntryExt2::file_name_ref(&self) -> &OsStr

DirEntryExt2 is a new trait with the same purpose as DirEntryExt,
but sealed

library/std/src/sys/unix/fs.rs

@@ -647,6 +647,10 @@ impl DirEntry {
     fn name_bytes(&self) -> &[u8] {
         &*self.name
     }
+
+    pub fn file_name_os_str(&self) -> &OsStr {
+        OsStr::from_bytes(self.name_bytes())
+    }
 }
 
 impl OpenOptions {