input-a2.component.ts

@Component({
  template: `...<button (click)="clear()">X</button>`
})
export class InputComponent {
  ref: InputRefDirective;

  @ContentChild(InputRefDirective) set inputRef(ref: InputRefDirective) {
    this.ref = ref;
  }

  clear() {
    this.ref.control.patchValue('');
  }
}

@NgModule({
  declarations: [InputComponent, InputRefDirective],
  exports: [InputComponent, InputRefDirective]
})
export class InputModule {}

input-a3.component.ts

@Directive({
  selector: '[inputRef]'
})
export class InputRefDirective {
  constructor(@Optional() private ngControl: NgControl) {
  }

  get control() {
    return this.ngControl?.control;
  }
}