[php-src] Issue #15123: var_dump doesn't actually work on XMLReader

Issue: https://github.com/php/php-src/issues/15123 Author: nielsdos ### Description Discovered while working on virtual property improvements. In fact, it appears to have never worked. In 8.0 it just outputted an empty object: https://3v4l.org/qsVMP#v8.0.0 The following code: ```php <?php $reader = XMLReader::XML("<root>hi</root>"); while ($reader->read()) { var_dump($reader); } ``` Resulted in this output: ``` a bunch of uninitialized properties ``` But I expected this output instead: ``` not that ``` ### PHP Version 8.0+ ### Operating System _No response_