[cdk: subject] add cdk subject

[LaamGinghong]

API

• I have searched the issues of this repository and believe that this is not a duplicate.

What problem does this feature solve?

自己实现一个类rxjs Subject的事件发布订阅管理

What does the proposed API look like?

declare class Subject<T> {
  public dispatch: (value?: T) => void 
  
  public subscribe: ((value: T) => void) => void
}

[danranVm]

应该还有一个取消订阅的方法？