title: UIStackView contentHuggingPriority doesn't work for filling available space
body: <p>I want to create a chat bottom bar with the following content, in a horizontal <code>UIStackView</code>:</p>
  <ul>
  <li>a <code>UITextField</code> on the left side, taking all the available space</li>
  <li>a label on the right with fixed size (default intrinsic content size)</li>
  </ul>
  <p>Here is my code:</p>
  <pre><code>let messageTextField = UITextField()
  messageTextField.translatesAutoresizingMaskIntoConstraints = false
  messageTextField.setContentCompressionResistancePriority(.defaultHigh, for: .horizontal)
  messageTextField.setContentHuggingPriority(.defaultHigh, for: .horizontal)
  
  let label = UILabel()
  label.translatesAutoresizingMaskIntoConstraints = false
  label.text = &quot;SEND&quot;
  label.setContentHuggingPriority(.defaultLow, for: .horizontal)
  label.setContentCompressionResistancePriority(.required, for: .horizontal)
  label.textColor = .red
  
  let sv = UIStackView()
  sv.axis = .horizontal
  sv.distribution = .fill
  sv.alignment = .center
  sv.translatesAutoresizingMaskIntoConstraints = false
  
  // constraint the stack view to the bottomBar view 
  bottomBar.addSubview(sv)
  NSLayoutConstraint.activate([
      sv.leadingAnchor.constraint(equalTo: bottomBar.leadingAnchor, constant: 20),
      sv.trailingAnchor.constraint(equalTo: bottomBar.trailingAnchor, constant: -20),
      sv.bottomAnchor.constraint(equalTo: bottomBar.bottomAnchor, constant: -8),
      sv.topAnchor.constraint(equalTo: bottomBar.topAnchor, constant: 8)
  ])
  
  sv.addArrangedSubview(messageTextField)
  sv.addArrangedSubview(label)
  
  NSLayoutConstraint.activate([
      messageTextField.heightAnchor.constraint(equalTo:sv.heightAnchor),
      // I didn't put any width constraint for textField because it make no sense, as I want it to take all the available space on the right 
  ])
  </code></pre>
  <p>With this code, the label is expanding its size and filling all the available space on the right, and the text field is not showing (inspector says width = 0); exactly the opposite of what I want.</p>
  <p>I don't understand why it doesn't work because I explicitly configured it so it does not expand the label with:</p>
  <pre><code>label.setContentHuggingPriority(.defaultLow, for: .horizontal)
  </code></pre>
  <p>and instead to expand the text field with:</p>
  <pre><code>messageTextField.setContentHuggingPriority(.defaultHigh, for: .horizontal)
  </code></pre>
  <p>What did I miss here? I have read through many SO answers, Apple documentation, and followed various tutorials and videos, but I'm not able to achieve this seemingly simple thing.</p>