PHP 8.1 fixes

PHP 8.1 doesn't like unset array indices, like $definition['field_types'] and $definition['settings'] that can be unset.

Change:

      else {
        $field_types = array_merge($field_types, $definition['field_types']);
      }

      $field_info['field_types'] = NestedArray::mergeDeep($field_info['field_types'], $field_types);
      $field_info['settings'] = NestedArray::mergeDeep($field_info['settings'], $definition['settings']);

to:

      else {
        if (isset($definition['field_types'])) {
          $field_types = array_merge($field_types, $definition['field_types']);
        }
      }

      $field_info['field_types'] = NestedArray::mergeDeep($field_info['field_types'], $field_types);
      if (isset($definition['settings'])) {
        $field_info['settings'] = NestedArray::mergeDeep($field_info['settings'], $definition['settings']);
      }