code: public static function findValuesAddedToEnums(
          Schema $oldSchema,
          Schema $newSchema
      ) {
          $oldTypeMap = $oldSchema->getTypeMap();
          $newTypeMap = $newSchema->getTypeMap();
  
          $valuesAddedToEnums = [];
          foreach ($oldTypeMap as $typeName => $oldType) {
              $newType = $newTypeMap[$typeName] ?? null;
              if (! ($oldType instanceof EnumType) || ! ($newType instanceof EnumType)) {
                  continue;
              }
              $valuesInOldEnum = [];
              foreach ($oldType->getValues() as $value) {
                  $valuesInOldEnum[$value->name] = true;
              }
              foreach ($newType->getValues() as $value) {
                  if (isset($valuesInOldEnum[$value->name])) {
                      continue;
                  }
  
                  $valuesAddedToEnums[] = [
                      'type'        => self::DANGEROUS_CHANGE_VALUE_ADDED_TO_ENUM,
                      'description' => sprintf('%s was added to enum type %s.', $value->name, $typeName),
                  ];
              }
          }
  
          return $valuesAddedToEnums;
      }
docs: Given two schemas, returns an Array containing descriptions of any dangerous
  changes in the newSchema related to adding values to an enum type.
  
  @return string[][]