title: searchable modifier not displaying search bar below navigation bar title
body: <p>I'm using iOS 15 and trying out the new <code>searchable</code> modifier on Lists in SwiftUI. It looks like when you attach <code>searchable(text: $searchText)</code> to a NavigationView the search bar renders on the screen by default below the navigation bar title. When I've tried using it and I run the simulator, the search bar isn't rendered on the screen. Only when I start scrolling down on the screen through the list, does the search bar appear on the screen.</p>
  <p>Is this expected behavior?</p>
  <p>Here's the code.</p>
  <pre class="lang-swift prettyprint-override"><code>@State private var searchText = &quot;&quot;
  let data = (1...50).map( {_ in Int.random(in: 1...10)} )
  
  var body: some View {
      NavigationView {
          List {
              ForEach(data, id: \.self) { d in
                  Text(&quot;\(d)&quot;)
              }
          }
      }.searchable(text: $searchText)
  }
  </code></pre>
  <p>Before scrolling</p>
  <p><a href="https://i.stack.imgur.com/6dfhh.png" rel="noreferrer"><img src="https://i.stack.imgur.com/6dfhh.png" alt="enter image description here" /></a></p>
  <p>After scrolling</p>
  <p><a href="https://i.stack.imgur.com/Vymbv.png" rel="noreferrer"><img src="https://i.stack.imgur.com/Vymbv.png" alt="enter image description here" /></a></p>