message: Use contentWidth to calculate btnCancel position
  This avoids the need to pre-set the size of the window, as we no longer
  use the window size() method.
diff: @@ -63,7 +63,7 @@ RobotInspector::RobotInspector() :
  add(btnSelfDestruct, buttonPosition);
  btnCancel.size({ mainFont.width(constants::ButtonCancel) + padding, buttonHeight });
  - buttonPosition = { rect().width - btnCancel.size().x - constants::MARGIN, buttonPosition.y + buttonOffsetY * 2 };
  + buttonPosition = { contentWidth - btnCancel.size().x, buttonPosition.y + buttonOffsetY * 2 };
  add(btnCancel, buttonPosition);
  size({ size().x, buttonPosition.y + buttonHeight + constants::MARGIN });
  