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_setFlags_basic1.phpt

@@ -0,0 +1,51 @@
+--TEST--
+SPL: ArrayObject::setFlags basic usage with ArrayObject::ARRAY_AS_PROPS. Currently fails on php.net due to bug 45622.
+--FILE--
+<?php
+class C extends ArrayObject {
+    public $p = 'object property';
+}
+
+function access_p($ao) {
+  // isset
+  var_dump(isset($ao->p));
+  // read
+  var_dump($ao->p);
+  // write
+  $ao->p = $ao->p . '.changed';
+  var_dump($ao->p);
+}
+
+$ao = new C(array('p'=>'array element'));
+$ao->setFlags(ArrayObject::ARRAY_AS_PROPS);
+
+echo "\n--> Access the real property:\n";
+access_p($ao);
+
+echo "\n--> Remove the real property and access the array element:\n";
+unset($ao->p);
+access_p($ao);
+
+echo "\n--> Remove the array element and try access again:\n";
+unset($ao->p);
+access_p($ao);
+?>
+--EXPECTF--
+--> Access the real property:
+bool(true)
+string(15) "object property"
+string(23) "object property.changed"
+
+--> Remove the real property and access the array element:
+bool(true)
+string(13) "array element"
+string(21) "array element.changed"
+
+--> Remove the array element and try access again:
+bool(false)
+
+Warning: Undefined array key "p" in %s on line %d
+NULL
+
+Warning: Undefined array key "p" in %s on line %d
+string(8) ".changed"