title: Why does UIStackView not stack a UILabel arrangedSubview?
body: <p>I have a UIStackView, and as arranged subviews, I have two UIViews, and a UILabel. The UIViews are stacked one after another, while the UILabel is aligned to the leading edge of the subview. </p>
  
  <p>Code:</p>
  
  <pre><code>let stack = UIStackView()
  stack.axis = .horizontal
  stack.distribution = .fillProportionally
  stack.alignment = .center
  stack.spacing = 7
  view.addSubview(stack)
  stack.translatesAutoresizingMaskIntoConstraints = false
  stack.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true
  stack.centerYAnchor.constraint(equalTo: view.centerYAnchor).isActive = true
  
  let icon = UIView()
  icon.backgroundColor = UIColor.red
  stack.addArrangedSubview(icon)
  icon.translatesAutoresizingMaskIntoConstraints = false
  icon.heightAnchor.constraint(equalToConstant: 42).isActive = true
  icon.widthAnchor.constraint(equalToConstant: 42).isActive = true
  
  let icon2 = UIView()
  icon2.backgroundColor = UIColor.red
  stack.addArrangedSubview(icon2)
  icon2.translatesAutoresizingMaskIntoConstraints = false
  icon2.heightAnchor.constraint(equalToConstant: 42).isActive = true
  icon2.widthAnchor.constraint(equalToConstant: 42).isActive = true
  
  let label = UILabel()
  label.lineBreakMode = .byWordWrapping
  label.numberOfLines = 0
  label.sizeToFit()
  label.translatesAutoresizingMaskIntoConstraints = false
  label.backgroundColor = .yellow
  label.text = "Hello World! Again"
  label.textColor = .black
  stack.addArrangedSubview(label)
  </code></pre>
  
  <p>Output:
  <a href="https://i.stack.imgur.com/0xV6M.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/0xV6M.png" alt="enter image description here"></a></p>