message: Add range box to ground plane.
  Makes it easier to determine if viewing tools - particularly rotate -
  are behaving as expected.
diff: @@ -1159,8 +1159,9 @@ export abstract class ViewState3d extends ViewState {
  const ellipse = Arc3d.createXYEllipse(center, Math.abs(center.x - extents.low.x), Math.abs(center.y - extents.low.y));
  const gf = context.createWorldDecoration();
  const green = ColorDef.green.clone();
  - gf.setSymbology(green, green, 1);
  + gf.setSymbology(green, green, 2);
  gf.addArc(ellipse, true, true);
  + gf.addRangeBox(extents);
  context.addWorldDecoration(gf.finish()!);
  }
  }
  