title: VirtualStringTree columns should adapt size when one column is hidden
body: <p>I have a VST with 3 columns that evenly take the available space.</p>
  <ul>
  <li>I have set <code>hoAutoSpring</code> in <strong>Header.Options</strong>, and</li>
  <li>all columns have <strong>Column[x].Option</strong> have <code>coAutoSpring</code> set.</li>
  </ul>
  <p>Now I want to be able to hide the last column and maintain that the other columns evenly take the free space (a little bit like a control with <code>alClient</code>).</p>
  <p>When I only set the column invisible (see below) the space that was taken by the column is then simply unused.</p>
  <pre><code>VST.Header.Columns[2].Options:=VST.Header.Columns[2].Options - [coVisible];
  </code></pre>
  <p>When I set <strong>Header.Options.hoAutoResize</strong> to <strong>True</strong> and set <strong>Header.AutoSizeIndex</strong> to <code>1</code>, then the 2nd Column will take all the new space.</p>
  <p>Is there a method to tell the columns to fill up the available space and resize evenly?</p>
  <p>Screenshot:</p>
  <p><img src="https://i.stack.imgur.com/vuBFj.png" alt="enter image description here" /></p>