code: function processErrors (errors, transformers) {
    const transform = (error, transformer) => transformer(error);
    const applyTransformations = (error) => transformers.reduce(transform, error);
  
    return errors.map(extractError).map(applyTransformations);
  }
docs: Applies all transformers to all errors and returns "annotated"
  errors.
  
  Each transformer should have the following signature WebpackError => AnnotatedError
  
  A WebpackError has the following fields:
  - message
  - file
  - origin
  - name
  - severity
  - webpackError (original error)
  
  An AnnotatedError should be an extension (Object.assign) of the WebpackError
  and add whatever information is convenient for formatting.
  In particular, they should have a 'priority' field.
  
  The plugin will only display errors having maximum priority at the same time.
  
  If they don't have a 'type' field, the will be handled by the default formatter.