[11.x] Expose process checkTimeout method

[mattmcdev]

This PR targets the same issue as this #54903 but without any breaking changes.

It just exposes the checkTimeout method and throws the same exception as wait would if the process has timed out.

This would update ensure the example use of Process::timeout() actually does something.

$process = Process::timeout(120)->start('bash import.sh');
 
while ($process->running()) {
    $process->checkTimeout()

    // ... 
}
 
$result = $process->wait();

As of right now, setting Process::timeout(x) and using $process->running as documented is pointless as the timeout will never happen.