Implement Long Tasks API for PerformanceObserver (#45473)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/45473

This is a basic implementation of the Long Tasks API (https://w3c.github.io/longtasks/).

It detects and reports long tasks when using the Event Loop (in the modern RuntimeScheduler) when a new feature flag for this purpose is enabled.

This doesn't include attribution information at the moment.

Changelog: [internal]

Reviewed By: sammy-SC

Differential Revision: D55491870

fbshipit-source-id: e1ccad9cc6a35073b31230a8cf3a4660ab9a043d