Support async ErrorStateMatcher

#### Please describe the feature you would like to request.

Currently, `ErrorStateMatcher` doesn't support return type `Promise` and `Observable`. Its return type is only `boolean`.

#### What is the use-case or motivation for this proposal?

I need to show `` when checked `input` is invalid after validation. This validation does need to call HTTP request(async). For example, when ID field in registration form is not unique, i should show `` because registration form doesn't allow to use the input's value as duplicated ID with other user. To provide this feature, `ErrorStateMatcher` has to support return type as `Promise` or `Observable`.

Inizia leggendo l'API ErrorStateMatcher e il flusso di convalida mat-error esistente, concentrandoti su come viene verificata la validità dell'input. Confronta i casi richiesti di Promise e Observable, quindi definisci il completamento in modo che i risultati della convalida asincrona causino in modo affidabile lo stato mat-error appropriato per gli ID duplicati.

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