[php-src] Issue #10648: mb_check_encoding() returns true for incorrect but interpretable ISO-2022-JP byte sequences

Issue: https://github.com/php/php-src/issues/10648 Author: pakutoma ### Description Since PHP 8.1, mb_check_encoding returns true for many incorrect but interpretable ISO-2022-JP (JIS) byte sequences. For example, IETF RFC 1468, often referenced as the definition of ISO-2022-JP, says "the text must end in ASCII." https://datatracker.ietf.org/doc/html/rfc1468 This means that an ISO-2022-JP byte sequence must end with the escape sequence 0x1b 0x28 0x42 to switch to ASCII. However, mb_check_encoding() returns true without the escape sequence in PHP 8.1 and later. The documentation says it returns true when "valid", but what should mb_check_encoding return in such a case? https://www.php.net/manual/en/function.mb-check-encoding.php 3v4l: https://3v4l.org/9i19F The following code: ```php <?php $jis_bytes = '1b244224221b2842'; // 'あ' in ISO-2022-JP $jis_bytes_without_esc = '1b24422422'; // 'あ' in ISO-2022-JP without escape sequence var_dump(mb_check_encoding(hex2bin($jis_bytes), 'JIS')); var_dump(mb_check_encoding(hex2bin($jis_bytes_without_esc), 'JIS')); ``` Resulted in this output: ``` bool(true) bool(true) ``` But I expected this output instead: ``` bool(true) bool(false) ``` ### PHP Version PHP 8.1.16 ### Operating System _No response_