[php-src] Issue #8281: mb_convert_encoding "\" (backslash) and "~" (tilde) convert failed to Shift_JIS

Issue: https://github.com/php/php-src/issues/8281 Author: youkidearitai ### Description Backslash(\\) and tilde(~) is convert to Shift_JIS (SJIS) using mb_convrert_encoding, But converted word is wrong word. Please see below code and 3v4l <https://3v4l.org/nSVPB>. Reproduced only PHP 8.1. The following code: ```php <?php var_dump(mb_convert_encoding(mb_convert_encoding("\\", "SJIS", "UTF-8"), "UTF-8", "SJIS")); var_dump(mb_convert_encoding(mb_convert_encoding("~", "SJIS", "UTF-8"), "UTF-8", "SJIS")); ``` Resulted in this output: ``` string(3) "＼" string(3) "〜" ``` But I expected this output instead: ``` string(1) "\" string(1) "~" ``` ### PHP Version PHP 8.1.4 ### Operating System _No response_