[Android] Add ClearTop and NewTask flags when using Device.OpenUri (#3503) fixes #3477

Xamarin.Forms.Platform.Android/Forms.cs

@@ -520,6 +520,8 @@ namespace Xamarin.Forms
 			{
 				global::Android.Net.Uri aUri = global::Android.Net.Uri.Parse(uri.ToString());
 				var intent = new Intent(Intent.ActionView, aUri);
+				intent.SetFlags(ActivityFlags.ClearTop);
+				intent.SetFlags(ActivityFlags.NewTask);
 
 				// This seems to work fine even if the context has been destroyed (while another activity is in the
 				// foreground). If we run into a situation where that's not the case, we'll have to do some work to