Context passed to emulated auth.onCreate is not a valid EventContext

### [REQUIRED] Environment info

**firebase-tools:8.14.1**

**Platform:macOS**

### [REQUIRED] Test case

```
functions
.auth.user()
.onCreate(userRecord, context) => {
console.log(context)
}
```

### [REQUIRED] Steps to reproduce

Include the above snippet as a cloud function and create a new user. You'll see that the `context` is not a valid `EventContext`.

### [REQUIRED] Expected behavior

I would expect `context` to contain all properties specified in `EventContext`.

### [REQUIRED] Actual behavior

`context` is missing e.g. the `eventId` and the `timestamp`. See the log output:
```
{
eventType: 'google.firebase.auth.user.create',
resource: { service: 'firebaseauth.googleapis.com', name: undefined },
params: {}
}
```