Add `mixed` type to verified type checks

[Ocramius]

We need to add the mixed type to ClassWithMixedReferenceableTypedProperties.

Specifically, nullability checks around mixed are a bit interesting (because mixed|null doesn't really exist for PHP).

Potentially just some additions to

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;