When implemented in a derived class, gets a unique identifier for this attribute.
Implemented in xtd::reflection::assembly_company_attribute, xtd::reflection::assembly_configuration_attribute, xtd::reflection::assembly_copyright_attribute, xtd::reflection::assembly_culture_attribute, xtd::reflection::assembly_description_attribute, xtd::reflection::assembly_file_version_attribute, xtd::reflection::assembly_guid_attribute, xtd::reflection::assembly_identifier_attribute, xtd::reflection::assembly_name_attribute, xtd::reflection::assembly_product_attribute, xtd::reflection::assembly_title_attribute, xtd::reflection::assembly_trademark_attribute, and xtd::reflection::assembly_version_attribute.