#2181361 Moved FAPI callbacks for file/image widgets in classes

from:
  fqn: 'fn:file_field_widget_value'
to:
  fqn: '\Drupal\file\Plugin\Field\FieldWidget\FileWidget::value'
from:
  fqn: 'fn:file_field_widget_multiple_count_validate'
to:
  fqn: '\Drupal\file\Plugin\Field\FieldWidget\FileWidget::validateMultipleCount'
from:
  fqn: 'fn:file_field_widget_process'
to:
  fqn: '\Drupal\file\Plugin\Field\FieldWidget\FileWidget::process'
from:
  fqn: 'fn:file_field_widget_process_multiple'
to:
  fqn: '\Drupal\file\Plugin\Field\FieldWidget\FileWidget::processMultiple'
from:
  fqn: 'fn:_file_field_get_description_from_element'
to:
  fqn: '\Drupal\file\Plugin\Field\FieldWidget\FileWidget::getDescriptionFromElement'
from:
  fqn: 'fn:file_field_widget_submit'
to:
  fqn: '\Drupal\file\Plugin\Field\FieldWidget\FileWidget::submit'
from:
  fqn: 'fn:image_field_widget_process'
to:
  fqn: '\Drupal\image\Plugin\Field\FieldWidget\ImageWidget::process'
from:
  fqn: 'fn:_image_field_required_fields_validate'
to:
  fqn: '\Drupal\image\Plugin\Field\FieldWidget\ImageWidget::validateRequiredFields'