code: def _FetchCustomMappings(descriptor_ls):
      
      custom_mappings = []
      for descriptor in descriptor_ls:
          if isinstance(descriptor, ExtendedEnumDescriptor):
              custom_mappings.extend(
                  _FormatCustomJsonMapping('Enum', m, descriptor)
                  for m in descriptor.enum_mappings)
          elif isinstance(descriptor, ExtendedMessageDescriptor):
              custom_mappings.extend(
                  _FormatCustomJsonMapping('Field', m, descriptor)
                  for m in descriptor.field_mappings)
              custom_mappings.extend(
                  _FetchCustomMappings(descriptor.enum_types))
              custom_mappings.extend(
                  _FetchCustomMappings(descriptor.message_types))
      return custom_mappings
docs: Find and return all custom mappings for descriptors in descriptor_ls.