Description:
------------
Hello.

ReflectionObject::getProperties() returns property which added to ArrayObject with offsetSet(), but this property can't be gotten by ReflectionProperty::getValue().

See https://3v4l.org/Y2CkO

Test script:
---------------
<?php

class A extends \ArrayObject {}

$a = new A;
$a->offsetSet('test', 'testValue');

$reflection = new \ReflectionObject($a);
$properties = $reflection->getProperties();

$c = count($properties);

echo $c . PHP_EOL;

if ($c) {
    echo $properties[0]->getValue($a) . PHP_EOL;
}

Expected result:
----------------
I'm not sure what is expected behaviour, but it's strange to have abiliti get property of ArrayObject and have not ability to get value of this property.

Variants:
1. Properties have not be returned by ReflectionObject::getProperties()
------ EXPECTED -----
1
testValue
------ EXPECTED -----


2. Property values should be accessible by ReflectionProperty::getValue()
------ EXPECTED -----
0
------ EXPECTED -----

Actual result:
--------------
1

Notice: Undefined property: A::$test in /in/FbMbQ on line 14