Expose network throttling capability to frontend

Summary:
Expose the simulated network throttling capability to the React Native DevTools frontend by adding an `unstable_networkThrottlingEnabled` boolean to the `ReactNativeApplication.metadataUpdated` CDP event payload. This mirrors the existing `unstable_networkInspectionEnabled`, `unstable_frameRecordingEnabled` etc fields, letting the frontend gate its throttling UI on whether the backend supports `Network.emulateNetworkConditions`.

See also react/react-native-devtools-frontend#279.

Changelog: [Internal]

Differential Revision: D111725569

Author: huntie

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

@@ -328,6 +328,7 @@ namespace {
 struct StaticHostTargetMetadata {
   std::optional<bool> isProfilingBuild;
   std::optional<bool> networkInspectionEnabled;
+  std::optional<bool> networkThrottlingEnabled;
   std::optional<bool> frameRecordingEnabled;
 };
 
@@ -337,6 +338,7 @@ StaticHostTargetMetadata getStaticHostMetadata() {
   return {
       .isProfilingBuild = inspectorFlags.getIsProfilingBuild(),
       .networkInspectionEnabled = true,
+      .networkThrottlingEnabled = inspectorFlags.getNetworkThrottlingEnabled(),
       .frameRecordingEnabled = inspectorFlags.getFrameRecordingEnabled()};
 }
 
@@ -372,6 +374,10 @@ folly::dynamic createHostMetadataPayload(const HostTargetMetadata& metadata) {
     result["unstable_networkInspectionEnabled"] =
         staticMetadata.networkInspectionEnabled.value();
   }
+  if (staticMetadata.networkThrottlingEnabled) {
+    result["unstable_networkThrottlingEnabled"] =
+        staticMetadata.networkThrottlingEnabled.value();
+  }
   if (staticMetadata.frameRecordingEnabled) {
     result["unstable_frameRecordingEnabled"] =
         staticMetadata.frameRecordingEnabled.value();

packages/react-native/ReactCommon/jsinspector-modern/tests/JsiIntegrationTest.cpp

@@ -360,7 +360,8 @@ TYPED_TEST(JsiIntegrationPortableTest, ReactNativeApplicationEnable) {
                                             "integrationName": "JsiIntegrationTest",
                                             "unstable_frameRecordingEnabled": false,
                                             "unstable_isProfilingBuild": false,
-                                            "unstable_networkInspectionEnabled": true
+                                            "unstable_networkInspectionEnabled": true,
+                                            "unstable_networkThrottlingEnabled": false
                                           }
                                         })"));