add ArrayAccess to SimpleXmlElement (#4934)

* add ArrayAccess to SimpleXmlElement

* add test

stubs/CoreGenericClasses.phpstub

@@ -2215,7 +2215,7 @@ final class WeakReference
     public function get(): ?object;
 }
 
-class SimpleXMLElement implements \Stringable, \Countable, \RecursiveIterator
+class SimpleXMLElement implements \Stringable, \Countable, \RecursiveIterator, \ArrayAccess
 {
     /** @return array */
     public function getNamespaces(bool $recursive = false)
@@ -2284,6 +2284,22 @@ class SimpleXMLElement implements \Stringable, \Countable, \RecursiveIterator
     public function getChildren()
     {
     }
+
+    public function offsetExists($offset)
+    {
+    }
+
+    public function offsetGet($offset)
+    {
+    }
+
+    public function offsetSet($offset, $value)
+    {
+    }
+
+    public function offsetUnset($offset)
+    {
+    }
 }
 
 interface Serializable {

tests/ArrayAccessTest.php

@@ -835,6 +835,14 @@ class ArrayAccessTest extends TestCase
                         return $s["a"];
                     }',
             ],
+            'simpleXmlArrayFetchChildren' => [
+                '<?php
+                    function iterator(SimpleXMLElement $xml): iterable {
+                        foreach ($xml->children() as $img) {
+                            yield $img["src"] ?? "";
+                        }
+                    }',
+            ],
             'assertOnArrayAccess' => [
                 '<?php
                     class A {