Restore inspector addPage listener callback (react#55925)

Summary:
Pull Request resolved: react#55925

Accidentally clobbered in D93247603. This affects the `fuseboxAssertSingleHostState` feature (react/react-native-devtools-frontend#218).

Changelog: [Internal]

Reviewed By: vzaidman

Differential Revision: D95365621

fbshipit-source-id: 0df7f7bb33bb6bf6eabe15c8ee06c1761567c84b

Author: huntie

packages/react-native/ReactCommon/jsinspector-modern/InspectorInterfaces.cpp

@@ -143,13 +143,9 @@ int InspectorImpl::addPage(
       pageId,
       Page{pageId, description, vm, std::move(connectFunc), capabilities});
 
-  // Strong assumption: If prefersFuseboxFrontend is set, the page added is a
-  // HostTarget and not a legacy Hermes runtime target.
-  if (capabilities.prefersFuseboxFrontend) {
-    for (const auto& listenerWeak : listeners_) {
-      if (auto listener = listenerWeak.lock()) {
-        listener->unstable_onHostTargetAdded();
-      }
+  for (const auto& listenerWeak : listeners_) {
+    if (auto listener = listenerWeak.lock()) {
+      listener->unstable_onHostTargetAdded();
     }
   }