Side Nav - fullscreen should make the side nav full screen only when its open

#### Feature Description

The `fullscreen` api of `mat-sidenav-container` allow us to show the side nav with height set to 100% of the viewport. And this probably is the most followed way to achieve this as proposed by these answers on stack overflow:

https://stackoverflow.com/questions/37334853/cant-get-angular-material-md-sidenav-to-be-100-height
https://stackoverflow.com/questions/46666381/unable-to-set-the-height-of-a-angular-material-sidenav-to-100

`fullscreen` option sets the below css properties on `mat-sidenav-container`:

```
top: 0!important;
left: 0!important;
right: 0!important;
bottom: 0!important;
position: absolute!important;
```

As a side effect I believe this blocks the scroll events and as a result it breaks the functionality of components/directives that relies on scroll events. For example, `ngx-infinite-scroll` is one of the commonly used plugins (87k weekly downloads) that allow loading contents as soon as user reaches to the bottom of the page. When we set `fullscreen` on `mat-sidenav-container` , `ngx-infinite-scroll` no longer works. As reported here

https://stackoverflow.com/questions/50377502/angular-material-and-ngx-infinite-scroll?rq=1

and

https://github.com/orizens/ngx-infinite-scroll/issues/182

What if we apply the below styles of `fullscreen` mode **only** when the side nav is opened:

```
top: 0!important;
left: 0!important;
right: 0!important;
bottom: 0!important;
position: absolute!important;
```

This way it wont affect the other portion of the application. Because when the nav bar is open user wont be scrolling the page contents, so if the scroll events are blocked it wont be a issue.

Beginne mit der mat-sidenav-container fullscreen API und reproduziere die gemeldete Interaktion mit ngx-infinite-scroll unter Verwendung der verlinkten Beispiele und Berichte als Kontext. Als erledigt gilt die Aufgabe, wenn die Fullscreen-Stile auf den Container angewendet werden, während die Side Nav geöffnet ist, ohne Seiten-Scroll-Ereignisse zu verhindern, wenn sie geschlossen ist.

Vom Indexierungsmodell aus dem Issue-Text verfasst.