title: Allow raw filter to work on label variable in twig's block view
body: <p>What I'm trying to achieve is to set the raw filter on my label element so that if in the CMS the user decide to put HTML tags, it works. When I try to do it, it doesn't seem to do anything (it stills flushes the HTML tag). I'm wondering if the label variable is pre-processed by Drupal in xxx.theme? Anyways, if you guys have any idea on how I could allow the <br /> tags in these, it would be the best.</p>
  
  <p>What I tried so far was to add the <a href="https://twig.symfony.com/doc/2.x/filters/raw.html" rel="nofollow noreferrer">raw</a> twig tag.</p>
  
  <pre><code>{#
  /**
   * @file
   * Default theme implementation to display a block.
   *
   * Available variables:
   * - plugin_id: The ID of the block implementation.
   * - label: The configured label of the block if visible.
   * - configuration: A list of the block's configuration values.
   *   - label: The configured label for the block.
   *   - label_display: The display settings for the label.
   *   - provider: The module or other provider that provided this block plugin.
   *   - Block plugin specific settings will also be stored here.
   * - content: The content of this block.
   * - attributes: array of HTML attributes populated by modules, intended to
   *   be added to the main container tag of this template.
   *   - id: A valid HTML ID and guaranteed unique.
   * - title_attributes: Same as attributes, except applied to the main title
   *   tag that appears in the template.
   * - title_prefix: Additional output populated by modules, intended to be
   *   displayed in front of the main title tag that appears in the template.
   * - title_suffix: Additional output populated by modules, intended to be
   *   displayed after the main title tag that appears in the template.
   *
   * @see template_preprocess_block()
   *
   * @ingroup themeable
   */
  #}
  &lt;div{{ attributes }}&gt;
    {{ title_prefix }}
    {% if label %}
      &lt;h2{{ title_attributes }}&gt;{{ label | raw }}&lt;/h2&gt;
    {% endif %}
    {{ title_suffix }}
    {% block content %}
      {{ content }}
    {% endblock %}
  &lt;/div&gt;
  </code></pre>