The core goal here is to make sure the following works in light of some middleware process that makes setting the source more async than next tick:
```js
player.src('...');
player.ready(() => player.play());
```
In fact, given this change, we should even be able to do:
```js
player.src('...');
player.play();
```
Unlike #4665, which would have clarified/changed the meaning of "ready", it remains a reflection of the tech's state and we make better use of the ability to queue things on that state and on the middleware `setSource` process.
