Somewhat related to #576 and #526

At the moment, selectors only apply to ngModel and formControlName meaning for Angular reactive forms to work with inputs, they must use formControlName within a formGroup directive.

I would like to add [formControl] to the list of selectors so that reactive forms can be used without a parent formGroup.

Rationale:
Say you have a dumb component which implements an input:

@Component({
  selector: 'my-custom-input',
  template: `<TextField [formControl]="control">`
})
export class MyCustomInput {
  @Input() control: FormControl
}

Which is used by some parent component:

@Component({
  selector: 'my-parent-component',
  template: `<my-custom-input [control]="formGroup.get('someControl')"`
})
export class MyCustomInput {
  public formGroup: FormGroup;
  constructor() {
    this.formGroup = new FormGroup({ someControl: new FormControl('') })
  }
}

The above does not work with the latest nativescript-angular with the following error: "No value accessor for form control with unspecified name attribute".

Adding the directives in the PR makes the above example work.