php: Support alternative notation of octal number literal (0o prefix)

[nsfisis]

Part of #2169

Support alternative notation of octal number literal since PHP 8.1.

https://www.php.net/manual/en/migration81.new-features.php#migration81.new-features.core.octal-literal-prefix

Octal integers can now use an explicit 0o/0O prefix in integer literals, similarly to binary and hexadecimal integer literals.

<?php
014;  // Non-prefix octal literal
0o14; // Prefixed octal literal
?>

[tancnle]

Thanks, @nsfisis. LGTM 🚀