message: Add doc comment inside DirHandler
diff: @@ -202,6 +202,16 @@ trait EvalContextExtPrivate<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, '
  #[derive(Debug, Default)]
  pub struct DirHandler {
  + /// Directory iterators used to emulate libc "directory streams", as used in opendir, readdir,
  + /// and closedir.
  + ///
  + /// When opendir is called, a new allocation is made, a directory iterator is created on the
  + /// host for the target directory, and an entry is stored in this hash map, indexed by a
  + /// pointer to the allocation which represents the directory stream. When readdir is called,
  + /// the directory stream pointer is used to look up the corresponding ReadDir iterator from
  + /// this HashMap, and information from the next directory entry is returned. When closedir is
  + /// called, the ReadDir iterator is removed from this HashMap, and the allocation that
  + /// represented the directory stream is deallocated.
  streams: HashMap<Pointer<Tag>, ReadDir>,
  }
  