Add addXmlDeclaration parameter

[silnex]

Improve usability of the addXmlDeclaration parameter 😄

before

<?php
$xml = (new ArrayToXml($arr))->dropXmlDeclaration()->toXml();

after

<?php
$xml = ArrayToXml::convert($arr, addXmlDeclaration: false);

[freekmurze]

Thanks!