feat(cdk/scrolling): Scroll functions silently fail if the viewport is not yet fully initialized

#### Feature Description

`cdk-virtual-scroll-viewport`'s `scrollTo...` functions (like `scrollToIndex`) silently fail when the viewport is not yet initialized. Technically the functions are doing nothing wrong from a code standpoint, but since the component is not yet fully initialized, it is empty, so trying to scroll will do nothing meaningful. Sending back an error (or at least logging a warning to the console) if an empty viewport is scrolled would be helpful so that developers know that something went wrong.

This would be mitigated if we had an async option that managed the timing of scroll commands. See [this feature request](https://github.com/angular/components/issues/23715).

#### Use Case

This would improve every use case of the virtual scroller.

Inizia dagli entry point scrollTo... di cdk-virtual-scroll-viewport e verifica come vengono rappresentati l’inizializzazione e un viewport vuoto. Conferma con i maintainer se il comportamento definitivo debba essere un errore o un avviso nella console, quindi aggiungi una copertura mirata che dimostri che lo scorrimento prima dell’inizializzazione non fallisce più silenziosamente.

Scritto dal modello di indicizzazione a partire dal testo della issue.