@Directive({
  selector: 'mat-autocomplete[optionsScroll]'
})
export class OptionsScrollDirective {
  @Output('optionsScroll') scroll = new EventEmitter<IAutoCompleteScrollEvent>();
}

<my-element (someEvent)="data" />
@Output() someEvent...

<my-element (someEvent)="data" />
@Output('someEvent') myEventEmitter... // if you want to use a different name.