title: Remove default padding from FlexibleSpace title
body: <p><a href="https://i.stack.imgur.com/7Ozdq.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/7Ozdq.png" alt="enter image description here"></a></p>
  
  <p>Code:</p>
  
  <pre><code>CustomScrollView(
    slivers: &lt;Widget&gt;[
      SliverAppBar(
        expandedHeight: 200.0,
        flexibleSpace: FlexibleSpaceBar(
          title: Container(color: Colors.red, child: Text("Flexible title")),
          background: Image.asset("assets/chocolate.jpg", fit: BoxFit.cover),
        ),
      ),
      SliverList(delegate: SliverChildListDelegate(_buildChildren())),
    ],
  );
  </code></pre>
  
  <p>Why there is a default padding in the title. I used <code>Container</code> to bring contrast so that the margin can be visible easily. Even I tried using <code>centerTitle: false</code> and it didn't change anything. </p>