Simplify PerformanceTracer API and move processing to TracingAgent (#52934)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/52934

Changelog: [internal]

Right now, the `PerformanceTracer` API has a method to stop the trace and a separate one to collect serialized events. This refactors the API to return the collected events when calling `stopTracing` instead.

The caller (in this case `TracingAgent`) is responsible for serializing and sending the events in chunks through CDP.

Reviewed By: hoxyq

Differential Revision: D79271690

fbshipit-source-id: bdb48c80be4fd07d96e381e6bb4d099cae91f8de