title: Add Taxvat field to magento 2 checkout page
body: <p>I'm from Brazil, and here we use the "taxvat" customer field to store a number called "CPF". I managed to make the field appear on checkout by adding it to an layoutProcessor, like this:</p>
  
  <pre><code>      $shippingFields['taxvat'] = [
          'component' =&gt; 'Magento_Ui/js/form/element/abstract',
          'label' =&gt; __('CPF'),
          'config' =&gt; [
              'customScope' =&gt; 'shippingAddress',
              'template' =&gt; 'ui/form/field',
              'elementTmpl' =&gt; 'ui/form/element/input',
          ],
          'placeholder' =&gt; 'CPF *',
          'validation' =&gt; [
              'required-entry' =&gt; 1
          ],
          'provider' =&gt; 'checkoutProvider',
          'source' =&gt; 'customer.taxvat',
          'dataScope' =&gt; 'customer.taxvat',
          'sortOrder' =&gt; 1,
      ];
  </code></pre>
  
  <p>But, i don't know why, this field it's not saving on database. It only works if i save this field on customer form, not on checkout form.</p>
  
  <p>Anyone know what i'm missing?</p>
  
  <p>thanks!</p>