Analytics Logs Run with High Priority

### [REQUIRED] Describe your environment

* Browser version: Chrome 80
* Firebase SDK version: ^7.6.1-0
* Firebase Product: hosting, functions, analytics

### [REQUIRED] Describe the problem
When using `logEvent`, the event logging requests run with `high` priority. Therefore, when I want to make an HTTP request, and also log the user event at the same time, I get this network stack, where my intentional HTTP request has a "waiting" time, probably caused because another `high` priority requests happen at the same time.

This is NOT the case with Google Analytics.

#### Steps to reproduce:

```javascript
logEvent("an event");
setTimeout(() => fetch("my-api-url"), 0); // This happens in the next event loop
```

#### Fix:

Pull request #2635