Assertion error for any module defining its own field type category

Problem/Motivation

In FieldTypePluginManager we have this code

  /**
   * {@inheritdoc}
   */
  public function getGroupedDefinitions(array $definitions = NULL, $label_key = 'label') {
    $grouped_categories = $this->getGroupedDefinitionsTrait($definitions, $label_key);
    $category_info = \Drupal::moduleHandler()->invokeAll('field_type_category_info');
    foreach ($grouped_categories as $group => $definitions) {
      if (!isset($category_info[$group]) && $group !== static::DEFAULT_CATEGORY) {
        assert(FALSE, "\"$group\" must be defined in hook_field_type_category_info().");
        $grouped_categories[static::DEFAULT_CATEGORY] += $definitions;
        unset($grouped_categories[$group]);
      }
    }

    return $grouped_categories;
  }

With the asser(FALSE) here we're causing an Assertion error for any module that defines a field type plugin with its own category that isn't yet backed by a field_type_category_info hook.

We should instead be triggering a deprecation error so modules know they need to update

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet