title: Detect DragGesture cancelation in SwiftUI
body: <p>So I have a Rectangle with an added DragGesture and want to track gesture start, change and ending. The issue is when I put another finger on the Rectangle while performing the gesture, the first gesture stop calling onChange handler and does not fire onEnded handler. 
  Also the handlers doesn't fire for that second finger.</p>
  
  <p>But if I place third finger without removing previous two the handlers for that gesture start to  fire (and so on with even presses cancel out the odd ones)</p>
  
  <p>Is it a bug? Is there a way to detect that the first gesture was canceled?</p>
  
  <pre class="lang-swift prettyprint-override"><code>Rectangle()
    .fill(Color.purple)
    .gesture(
      DragGesture(minimumDistance: 0, coordinateSpace: .local)
        .onChanged() { event in
          self.debugLabelText = "changed \(event)"
        }
        .onEnded() { event in
          self.debugLabelText = "ended \(event)"
        }
    )
  </code></pre>