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_overloaded_object_incompatible.phpt

@@ -0,0 +1,28 @@
+--TEST--
+Objects with overloaded get_properties are incompatible with ArrayObject
+--FILE--
+<?php
+
+$ao = new ArrayObject([1, 2, 3]);
+try {
+    $ao->exchangeArray(new DateInterval('P1D'));
+} catch (Exception $e) {
+    echo $e->getMessage(), "\n";
+}
+var_dump($ao);
+
+?>
+--EXPECTF--
+Deprecated: ArrayObject::exchangeArray(): Using an object as a backing array for ArrayObject is deprecated, as it allows violating class constraints and invariants in %s on line %d
+Overloaded object of type DateInterval is not compatible with ArrayObject
+object(ArrayObject)#1 (1) {
+  ["storage":"ArrayObject":private]=>
+  array(3) {
+    [0]=>
+    int(1)
+    [1]=>
+    int(2)
+    [2]=>
+    int(3)
+  }
+}