Add async resource with hasRef to threadsafe functions

[kjvalencik]

Currently, this creates a new object and a new hasRef function on it for every newly created Channel.

Should we optimize this? We could create a single hasRef cached on InstanceData since it uses this. This could possibly be further optimized by creating a class with hasRef that is instantiated. Creating the async resource would look like:

• napi_get_instance_data. Get the cached NeonAsyncResource class.
• napi_new_instance. Create an instance of the class.
• napi_wrap. Wrap the class with the Arc<Mutex<State>> data.
• napi_type_tag. Type tag for safety when unwrapping.

It might be worth using #[track_caller] and track the line number in the resource name. That might help users find out which TSFN is keeping things up.

Resolves #948