title: Resizing UIStackView when hiding a subview?
body: <p>I have a UIStackView with the config below, when i hide its first subview i want it to shrink in height rather than redistributing the height of the existing cells to fill or leaving white space.</p>
  
  <p>Is there a way to achieve this? as currently it wont change in height despite hiding its contents</p>
  
  <pre><code> let headerStackView = UIStackView()
      headerStackView.backgroundColor = .clear
      headerStackView.axis = .vertical
      headerStackView.alignment = .fill
      headerStackView.distribution = .equalSpacing
      headerStackView.spacing = 0
      headerStackView.isUserInteractionEnabled = true
      headerStackView.translatesAutoresizingMaskIntoConstraints = false
  </code></pre>
  
  <p>Constraints</p>
  
  <pre><code>    headerStackView.snp.makeConstraints { (make) -&gt; Void in
         make.leading.trailing.bottom.equalToSuperview()
         make.top.equalTo(topView.snp.bottom)
      }
  </code></pre>
  
  <p>Hiding of subview (opposite for showing)</p>
  
  <pre><code>            UIView.animate(withDuration: 0.35) { [weak self] in
              headerStackView.arrangedSubviews.first.isHidden = true
              headerStackView.arrangedSubviews.first.alpha = 0
              self?.detailsHeaderView.headerStackView.layoutIfNeeded()
          }
  </code></pre>