title: Qt 5.9 QML How to show ScrollBar on key up/down in material style with Flickable TextArea
body: <p>I want to put some text in a <code>Flickable</code> that can also scroll using keys up and down. It works, but the scrollbar does not show when scrolling with keys after it has already faded. Mouse wheel scrolling works fine.</p>
  
  <p><code>-style universal</code> doesn't show<br>
  <code>-style material</code> doesn't show<br>
  <code>-style default</code> <em>does</em> show  </p>
  
  <p>here's my code:</p>
  
  <pre><code>import QtQuick 2.7
  import QtQuick.Controls 2.2
  
  ApplicationWindow
  {
      visible: true
      width: 640
      height: 480
  
      Flickable
      {
          anchors.fill: parent
          flickableDirection: Flickable.VerticalFlick
          focus: true
  
          TextArea.flickable: TextArea 
          {
              text:
  
          "Lorem ipsum dolor sit amet, consectetur adipisicing elit, " +
          "sed do eiusmod tempor incididunt ut labore et dolore magna " +
          "aliqua. Ut enim ad minim veniam, quis nostrud exercitation " +
          "ullamco laboris nisi ut aliquip ex ea commodo cosnsequat. " +
  
          "Lorem ipsum dolor sit amet, consectetur adipisicing elit, " +
          "sed do eiusmod tempor incididunt ut labore et dolore magna " +
          "aliqua. Ut enim ad minim veniam, quis nostrud exercitation " +
          "ullamco laboris nisi ut aliquip ex ea commodo cosnsequat. " +
  
          "Lorem ipsum dolor sit amet, consectetur adipisicing elit, " +
          "sed do eiusmod tempor incididunt ut labore et dolore magna " +
          "aliqua. Ut enim ad minim veniam, quis nostrud exercitation " +
          "ullamco laboris nisi ut aliquip ex ea commodo cosnsequat. " +
  
          "Lorem ipsum dolor sit amet, consectetur adipisicing elit, " +
          "sed do eiusmod tempor incididunt ut labore et dolore magna " +
          "aliqua. Ut enim ad minim veniam, quis nostrud exercitation " +
          "ullamco laboris nisi ut aliquip ex ea commodo cosnsequat. " ;
  
  
              font.pixelSize: 25
              wrapMode: TextArea.Wrap
              readOnly: true
          }
  
          ScrollBar.vertical: ScrollBar { id: scrollBar }
  
          // up/down keys described here:
          // https://doc-snapshots.qt.io/qt5-5.8/qml-qtquick-controls2-scrollbar.html
          Keys.onUpPressed: scrollBar.decrease()
          Keys.onDownPressed: scrollBar.increase()
  
      }
  }
  </code></pre>
  
  <p>Thanks for any help.</p>