Features

Would love to see the new features from Firestore integrated into AngularFire. Mainly "Aggregation Queries".

### Version info

**Angular:**

**Firebase:**

**AngularFire:**

**Other (e.g. Ionic/Cordova, Node, browser, operating system):**

### How to reproduce these conditions

**Failing test unit, Stackblitz demonstrating the problem**

**Steps to set up and reproduce**

**Sample data and security rules**

### Debug output

** Errors in the JavaScript console **

** Output from `firebase.database().enableLogging(true);` **

** Screenshots **

### Expected behavior

### Actual behavior

尚未确定任何文件、测试或入口点。首先查看 AngularFire 的 Firestore 集成和 Firebase 的 Aggregation Queries 文档；要视为完成，需要为所请求的功能定义 AngularFire API，并覆盖其行为。

由索引模型根据 Issue 内容生成。