API to dump entities from async runtime

[zaucy]

The current dump entities function takes in a registry ID which is not exposed in the async API. Most async implementations have a registry under the hood and could utilise that for easy implementation.

Here's the proposed API:

void ecsact_async_dump_entities(
	ecsact_dump_entities_callback callback,
	void*                         callback_user_data
);

It's unclear to me if this should be part of the serialize or async module. I'm leaning towards the async module.

It's also worth mentioning that this function may need to block, but if we can reasonbly document it being non-blocking or implementation defined that would be okay too. If we're doing non-blocking maybe we shoudl return an ecsact_async_request_id and if we're non-blocking then it should almost certainly be part of the async module.