AppCheck Build Error During Prerender for Angular SSR

### Version info

**Angular:** 13.0.3

**Firebase:** 9.6.4

**AngularFire:** 7.2.0

**Other (e.g. Ionic/Cordova, Node, browser, operating system):** Node 14

### How to reproduce these conditions
**Steps to set up and reproduce**

After setting up AppCheck as such:

```typescript

import { initializeAppCheck, provideAppCheck, ReCaptchaV3Provider } from '@angular/fire/app-check';

provideAppCheck(() => initializeAppCheck(getApp(), { provider: new ReCaptchaV3Provider(environment.recaptchaSiteKey), isTokenAutoRefreshEnabled: true })),
```

I am able to serve my application with both `yarn server` and `yarn dev:ssr` and I'm able to load the site with AppCheck seemingly working. However, when I try to run `yarn prerender`, I get the following error:

```
Unhandled Promise rejection: document is not defined ; Zone: ; Task: Promise.then ; Value: ReferenceError: document is not defined
```

Comienza con la inicialización de AppCheck mostrada en el issue y reproduce el fallo con `yarn prerender` bajo Angular SSR. Rastrea qué configuración de AppCheck accede a `document` durante el prerendering; se considera terminado cuando el prerendering se completa sin el error `document is not defined` y el serving y el SSR de desarrollo siguen funcionando.

Escrito por el modelo de indexación a partir del texto del issue.