Ship enableNativeEventTargetEventDispatching by default (#58450)

Summary:
Pull Request resolved: https://github.com/react/react-native/pull/58450

The renderer can dispatch events either through the legacy plugin-based system or through the W3C EventTarget API (addEventListener/dispatchEvent), gated behind the enableNativeEventTargetEventDispatching feature flag. Enabling it by default was previously blocked on the renderer, which did not carry the necessary changes until React 19.3.0. That sync has now landed, so flip the flag's default value to true and drop the TODO that tracked the blocker.

Fully removing the flag and the legacy dispatch path is left for a follow-up.

Changelog:
[General][Changed] - Enabled Web-based event dispatching refactor

Reviewed By: javache

Differential Revision: D119495069

fbshipit-source-id: 53ad5b88c8b5cdd11c3fd1ee27d0f147b83c41a9