Drupal 8 - PHP Script to list all fields on all content types of a certain type (ex. text_long)

list_text_long_fields.php

<?php

// get node types
$node_types = \Drupal::entityTypeManager()
  ->getStorage('node_type')
  ->loadMultiple();

$entityManager = \Drupal::service('entity_field.manager');

// for each content type, get the text_long fields for that content type
foreach(array_keys($node_types) as $key => $value) { 
  print_r(PHP_EOL . PHP_EOL . $value . PHP_EOL);

  $fields = $entityManager->getFieldDefinitions("node", $value);   
  $text_long_fields = array_filter(
    $fields, 
    function ($field_value, $field_key) {  
      // only keep fields of type 'text_long'      
      return (strpos($field_value->getType(), 'text_long') > -1);
    }, ARRAY_FILTER_USE_BOTH
  );

  print_r(array_keys($text_long_fields));
}