Add EventEmitter C++ bridging type (#44808)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/44808

Adds an `AsyncEventEmitter` class which can be used as a property of currently C++ only Turbo Modules to send type safe data back to JavaScript.

Adding support for ObjC / Java Turbo Modules is possible, straight forward and can be added as an afterthought.

It implements this interface
```
export type EventEmitter<T> = {
  addListener(handler: (T) => mixed): EventSubscription,
};
```

## Hybrid
It is a 'hybrid' object.

1.) You `addListener(handler: (T) => mixed)` in JavaScript for emitted events (coming from C++, native code)
2.) You `emit(...Arg)` events in C++, native code (getting sent to JavaScript)

## Changelog:

[General] [Added] - Add EventEmitter C++ bridging type

## Facebook:
Apps usually create custom functionality to achieve this kind of behavior - e.g. https://www.internalfb.com/code/fbsource/[e72bd42a028a]/arvr/js/apps/RemoteDesktopCompanion/shared/turbo_modules/TMSubscription.h

Reviewed By: javache

Differential Revision: D57424391

fbshipit-source-id: 4999cafe9daeac125712a4bb7679d7acb9a6c389