Send custom CDP Event to Frontend to prepare for displaying a trace (facebook#53079)

Summary:

# Changelog: [Internal]

We need this to notify Frontend, so it updates the local state before receiving `Tracing.dataCollected` events.

Corresponding change in CDT fork - facebook/react-native-devtools-frontend#199.

Reviewed By: sbuggay

Differential Revision: D79672598

Author: hoxyq

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

@@ -44,6 +44,8 @@ TracingAgent::TracingAgent(
       sessionState_(sessionState),
       hostTargetController_(hostTargetController) {
   if (traceRecordingToEmit.has_value()) {
+    frontendChannel_(
+        cdp::jsonNotification("ReactNativeApplication.traceRequested"));
     emitTraceRecording(std::move(traceRecordingToEmit.value()));
   }
 }