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_exchangeArray_basic1.phpt

@@ -0,0 +1,40 @@
+--TEST--
+SPL: ArrayObject::exchangeArray() and copy-on-write references
+--FILE--
+<?php
+$ao = new ArrayObject();
+$swapIn = array();
+$cowRef = $swapIn; // create a copy-on-write ref to $swapIn
+$ao->exchangeArray($swapIn);
+
+$ao['a'] = 'adding element to $ao';
+$swapIn['b'] = 'adding element to $swapIn';
+$ao['c'] = 'adding another element to $ao';
+
+echo "\n--> swapIn:  ";
+var_dump($swapIn);
+
+echo "\n--> cowRef:  ";
+var_dump($cowRef);
+
+echo "\n--> ao:  ";
+var_dump($ao);
+?>
+--EXPECTF--
+--> swapIn:  array(1) {
+  ["b"]=>
+  string(25) "adding element to $swapIn"
+}
+
+--> cowRef:  array(0) {
+}
+
+--> ao:  object(ArrayObject)#%d (1) {
+  ["storage":"ArrayObject":private]=>
+  array(2) {
+    ["a"]=>
+    string(21) "adding element to $ao"
+    ["c"]=>
+    string(29) "adding another element to $ao"
+  }
+}