Use "is sequence" Twig test to prevent fatal errors when looping on slots

Problem/Motivation

If you use Grid Row component in a view and you have only one result, you will get this fatal error:

Exception: Object of type Drupal\node\Entity\Node cannot be printed. in Drupal\Core\Template\TwigExtension->escapeFilter()

Because content is a single renderable, so we are looping on the renderable properties:

  {% for item in content %}
    {% set col_sizes = [col_xs, col_sm, col_md, col_lg, col_xl, col_xxl, spacing_margin_bottom] %}
    <div{{ create_attribute({'class': col_sizes}) }}>
      {{ item }}
    </div>
  {% endfor %}

Proposed resolution

Since Twig 3.11, there are 2 new tests: is sequence and is mapping, so we can use them to check if there is a single renderable and wrap it into a sequence before looping:

  {% set content = content is sequence ? content : [content] %}

However, we may need to wait the move to 5.1.x branch because the 5.0.x branch is still supporting Drupal 10.2:

• Drupal 9.5.1 > Twig 2.15 : https://git.drupalcode.org/project/drupal/-/blob/9.5.1/core/composer.json
• Drupal 10.3.4 > Twig 3.14 : https://git.drupalcode.org/project/drupal/-/blob/10.3.4/core/composer.json
• Drupal 11.0.3 > Twig 3.14 : https://git.drupalcode.org/project/drupal/-/blob/11.0.3/core/composer.json
• Drupal 11.1.0-dev > Twig 3.14 : https://git.drupalcode.org/project/drupal/-/blob/11.x/core/composer.json

This change need to be done everywhere there is a loop on a slot:

carousel/carousel.twig:    {% for slide in slides %}
grid_row/grid_row.twig:  {% for item in content %}
nav/nav.twig:    {% for pane in tab_content %}
table/table.twig:  {% for stripe in stripes %}
table/table.twig:  {% for colgroup in colgroups %}
table/table.twig:        {% for col in colgroup.cols %}

What else?