ext/spl: Deprecate ArrayObject and ArrayIterator with objects (#19420)

RFC: https://wiki.php.net/rfc/deprecations_php_8_5#deprecate_arrayobject_and_arrayiterator_with_objects

This also moves tests into a subfolder.

ext/spl/tests/ArrayObject/ArrayObject_get_object_vars.phpt

@@ -0,0 +1,31 @@
+--TEST--
+get_object_vars() on ArrayObject works on the properties of the ArrayObject itself
+--FILE--
+<?php
+
+class Test {
+    public $test;
+    public $test2;
+}
+
+class AO extends ArrayObject {
+    private $test;
+
+    public function getObjectVars() {
+        return get_object_vars($this);
+    }
+}
+
+$ao = new AO(new Test);
+var_dump(get_object_vars($ao));
+var_dump($ao->getObjectVars());
+
+?>
+--EXPECTF--
+Deprecated: ArrayObject::__construct(): Using an object as a backing array for ArrayObject is deprecated, as it allows violating class constraints and invariants in %s on line %d
+array(0) {
+}
+array(1) {
+  ["test"]=>
+  NULL
+}