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. 🙏_

从 Youtube Player 组件及其当前为 private 的 load 方法开始，并以链接的 ready-event issue 作为上下文。将完成定义为：提供一种公开的方式来确定 Player 是否已加载，以及一种以编程方式加载它的 public 方式，从而支持所描述的 button 用例。

由索引模型根据 Issue 内容生成。