fix for stuck extension sheets when dismissed by swipe (#1117)

* fix for stuck extension sheets when dismissed by swipe

* simplify dismiss action assignments

src/iOS.Core/Views/CustomPresentationControllerDelegate.cs

@@ -0,0 +1,22 @@
+using System;
+using Foundation;
+using UIKit;
+
+namespace Bit.iOS.Core.Views
+{
+    public class CustomPresentationControllerDelegate : UIAdaptivePresentationControllerDelegate
+    {
+        private readonly Action DismissModalAction;
+
+        public CustomPresentationControllerDelegate(Action dismissModalAction)
+        {
+            DismissModalAction = dismissModalAction;
+        }
+
+        [Export("presentationControllerDidDismiss:")]
+        public override void DidDismiss(UIPresentationController presentationController)
+        {
+            DismissModalAction?.Invoke();
+        }
+    }
+}