title: Extract translations from FormType in Symfony4
body: <p>Is it possible to extract placeholders and titles translations from FormType class in Symfony4 using console command php bin/console translation:update --force uz ?</p>
  
  <pre><code>  {
        $builder
            -&gt;add('title', null, [
                'attr' =&gt; ['placeholder' =&gt; 'job_title_placeholder'],
                'attr_translation_parameters' =&gt; [
                    'job_title_placeholder' =&gt; 'What needs to be done',
                ],
            ])
            -&gt;add('description', TextareaType::class, [
                'attr' =&gt; ['placeholder' =&gt; 'job_description_placeholder'],
                'attr_translation_parameters' =&gt; [
                    'job_description_placeholder' =&gt; 'Describe project details',
                ],
            ])
  </code></pre>
  
  <p>After successful extracting keys 'job_title_placeholder' and 'description_title_placeholder' are not added to translation file</p>