Create twig filters: |add_class and |set_attribute

This is related to #3301373: Create twig |add_suggestion filter

In conjunction with the |add_suggestion filter, themers typically want to set CSS classes on the field components to maintain proper BEM architecture.

The issue above has this discussion to add this functionality into that filter, but in a subsequent Slack conversation @lauriii suggested splitting it into its own |add_class filter, along with a |setAttribute filter.

This would enable something like

{{ content.field_event__links|add_suggestion('list')|add_class('event__link-list') }}
{# Produces: #}
<ul class="list event__link-list">
  <li><a href="/">foo</a></li>
  <li><a href="/">bar</a></li>
</ul>

and

{{ content.field_event__links|as('list')|add_class('event__link-list')|set_attribute('data-kitten', 'mila') }}
{# Produces: #}
<div class="field__items field--tags__items event__link-list"> data-kitten="mila">
  <!-- rest of the markup -->
</div>