napi async cleanup hook

Function pointer used with [napi_add_async_cleanup_hook][]. It will be called when the environment is being torn down.

Callback functions must satisfy the following signature:

typedef void (*napi_async_cleanup_hook)(napi_async_cleanup_hook_handle handle,
                                        void* data);

• [in] handle: The handle that must be passed to [napi_remove_async_cleanup_hook][] after completion of the asynchronous cleanup.
• [in] data: The data that was passed to [napi_add_async_cleanup_hook][].

The body of the function should initiate the asynchronous cleanup actions at the end of which handle must be passed in a call to [napi_remove_async_cleanup_hook][].