Freeze trim characters ahead of PHP 8.6

[GrahamCampbell]

PHP 8.6 adds the form feed character to the default $characters set of trim, ltrim, and rtrim, so calls relying on the default would change behavior there. This change passes the pre-8.6 set explicitly at the six call sites that relied on it, in the Linux binary auto-discovery, keyboard key normalization, and the browser process output handling, keeping behavior identical on every PHP version. An audit of the rest of the package found nothing else to fix: the remaining patterns already carry the PCRE D modifier or use no end anchor, and every preg_match failure path fails closed.