Verify support of `readonly` properties

[Ocramius]

readonly properties must be verified.

Taking ClassWithMixedReferenceableTypedProperties:

ProxyManager/tests/ProxyManagerTestAsset/ClassWithMixedReferenceableTypedProperties.php

Lines 1 to 16 in 95f9ccf

	<?php
	declare(strict_types=1);
	namespace ProxyManagerTestAsset;
	/**
	* Base test class to play around with mixed visibility properties with different type definitions
	*
	* @author Marco Pivetta <ocramius@gmail.com>
	* @license MIT
	*/
	class ClassWithMixedReferenceableTypedProperties
	{
	public static $publicStaticUnTypedProperty = 'publicStaticUnTypedProperty';
	public static $publicStaticUnTypedPropertyWithoutDefaultValue;

We need to add a ClassWithReadOnlyProperties, and integrate it in every test that uses ClassWithMixedReferenceableTypedProperties