add will disappear to life cycle listening

lib/container/boost_container.dart

@@ -30,6 +30,7 @@ import '../logger.dart';
 enum ContainerLifeCycle {
   Init,
   Appear,
+  WillDisappear,
   Disappear,
   Destroy,
   Background,

lib/container/container_coordinator.dart

@@ -236,6 +236,8 @@ class ContainerCoordinator {
   }
 
   bool _nativeContainerWillDisappear(String name, Map params, String pageId) {
+    performContainerLifeCycle(_createContainerSettings(name, params, pageId),
+        ContainerLifeCycle.WillDisappear);
     return true;
   }