Summary: Now instead of passing `reactTag` through the whole event pipeline, we store it inside `EventTargetWrapper` (and it does not leave `UIManagerBinding`). It helps with reducing the complexity of `EventEmitter` and will help us in migrating to JSI.
Reviewed By: sahrens
Differential Revision: D13123045
fbshipit-source-id: aa9ee94d5660ff3090369c1e55cf748d2e72b987