feat(Youtube Player): view loading status and load programmatically

### Feature Description

Since the ready event is not fired anymore (https://github.com/angular/components/issues/28834), I would like to know if the player has been loaded yet or not (still showing placeholder). Is there already an api for that? If so I did not find it.

Furthermore it would be great if there were a way to programmatically load the player.
(The load method is currently private to the player component.)

"Dirty" workaround:
I am accessing the placeholder via css selectors and dispatching a click event on them in order to trigger the player load.

### Use Case

Example use case: UI Button that will trigger the player to play.
=> The button label may change depending on the loaded status and the click might trigger the player to load and start.

_PS: Thanks for the wrapper component. 🙏_

Start with the Youtube Player component and its currently private load method, using the linked ready-event issue for context. Define completion as an exposed way to determine whether the player has loaded and a public way to load it programmatically, supporting the described button use case.

Written by the indexing model from the issue text.