message: Emit full spans in miri
diff: @@ -365,9 +365,8 @@ fn report_msg<'tcx>(
  err.span_note(frame_info.span, &frame_info.to_string());
  } else {
  let sm = sess.source_map();
  - let lo = sm.lookup_char_pos(frame_info.span.lo());
  - let filename = sm.filename_for_diagnostics(&lo.file.name);
  - err.note(format!("{frame_info} at {}:{}:{}", filename, lo.line, lo.col.0 + 1));
  + let span = sm.span_to_embeddable_string(frame_info.span);
  + err.note(format!("{frame_info} at {span}"));
  }
  }
  