title: Angular, how to set focus in a specific FormControl of FormArray
body: <p>lHow ca I set focus to a specific field in a formArray?</p>
  
  <p>this is the formArray:</p>
  
  <pre><code>    this.productForm = this.formBuilder.array([
       this.formBuilder.group({
       code: [null],
       description: [null],
       unitPrice: [null],
       qty: [null],
       discount: [null],
       vat: [null],
       total: [null],
       amount: [null],
       taxAmount: [null]
    })
  ]);
  </code></pre>
  
  <p>I can have a lot of this formGroup and I need to focus a specific description field.
  Is there a smart way in angular?</p>