Move event dispatch logic from FabricUIManager into SurfaceMountingManager (#56659)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/56659

Refactor: consolidate the event dispatch decision (enqueue vs direct dispatch) into `SurfaceMountingManager.dispatchEvent`, removing the 3-way branching from `FabricUIManager.receiveEvent`. The sync event path remains in `FabricUIManager`.

This moves `getEventEmitter`, `getViewExists`, and `enqueuePendingEvent` calls behind a single `dispatchEvent` entry point, making the ordering logic fully encapsulated in `SurfaceMountingManager`.

Changelog: [Internal]

Reviewed By: zeyap

Differential Revision: D103007280

fbshipit-source-id: 15eed04c0d936836d2fedeaff09254266c0f0528