[0.81]Fix crash in ABIViewManager::RemoveAllChildren during shutdown (#15633)

* Fix crash in ABIViewManager::RemoveAllChildren during shutdown

* Change files

---------

Co-authored-by: Harini Malothu <hmalothu@microsoft.com>

Author: HariniMalothu17

change/react-native-windows-b8b3e795-5d9c-4d59-b647-a3d20d92e91b.json

@@ -0,0 +1,7 @@
+{
+  "type": "none",
+  "comment": "Fix crash in ABIViewManager::RemoveAllChildren during shutdown",
+  "packageName": "react-native-windows",
+  "email": "hmalothu@microsoft.com",
+  "dependentChangeType": "none"
+}

vnext/Microsoft.ReactNative/ABIViewManager.cpp

@@ -190,8 +190,19 @@ void ABIViewManager::AddView(const xaml::DependencyObject &parent, const xaml::D
 }
 
 void ABIViewManager::RemoveAllChildren(const xaml::DependencyObject &parent) {
+  if (!parent) {
+    return;
+  }
+
   if (m_viewManagerWithChildren) {
-    m_viewManagerWithChildren.RemoveAllChildren(parent.as<xaml::FrameworkElement>());
+    auto fe = parent.try_as<xaml::FrameworkElement>();
+    if (fe) {
+      try {
+        m_viewManagerWithChildren.RemoveAllChildren(fe);
+      } catch (...) {
+        // External view manager may fail during shutdown if view is already disposed
+      }
+    }
   } else {
     Super::RemoveAllChildren(parent);
   }