[php-src] PR #25248: Fix GH-13243: intval() does not detect the "0o" octal prefix

Pull Request: https://github.com/php/php-src/pull/25248 Author: mlantz Fixes #13243 intval() with base 0 already detects the 0b binary prefix (and strtol() handles 0x), but the explicit octal prefix 0o/0O added in PHP 8.1 was not recognized: ```php var_dump(0o17); // int(15) var_dump(octdec("0o17")); // int(15) var_dump(intval("0o17", 0)); // int(0) -> now int(15) var_dump(intval("-0o17", 8)); // int(0) -> now int(-15) ``` This generalizes the existing 0b prefix handling in PHP_FUNCTION(intval) to also detect 0o/0O when $base is 0 or 8, including the sign, leading whitespace and overflow handling it already has. Scope notes: - The base 10 case from the original report (intval("-0b…") returning 0) matches documented behaviour. Positive "0b…" strings also return 0 in base 10, and negative or overflowing 0b/0x strings already work with base 0/2/16. That case is left unchanged. - Numeric strings and (int) casts are unaffected ((int) "0o17" stays 0), as specified by the [explicit octal notation RFC](https://wiki.php.net/rfc/explicit_octal_notation). The RFC does not mention intval(). - Targeting master because this changes behaviour that has never worked. Added an UPGRADING entry. Tests: new ext/standard/tests/general_functions/gh13243.phpt covers signs, whitespace, overflow, invalid input, other bases and casts, and checks that the existing 0b/0x/leading-zero behaviour is unchanged. It fails without the patch. With it, ext/standard/tests/general_functions/ and ext/standard/tests/math/ all pass.