Add support for class_exist check to avoid phpstan errors

# Bug report

Currently if you have a `class_exists` around something phpstan will still throw an error.

### Code snippet that reproduces the problem

https://phpstan.org/r/92454f28-a02b-48b6-8b63-ec17656a57cb

```php
if (class_exists(NOT_EXIT_CLASS::class)) {
    $bundles = new NOT_EXIT_CLASS();
}
```

### Expected output

PHPStan should not error. 