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_basic2.phpt

@@ -0,0 +1,32 @@
+--TEST--
+SPL: Ensure access to non-visible properties falls back to dimension access with ArrayObject::ARRAY_AS_PROPS.
+--FILE--
+<?php
+class C extends ArrayObject {
+    private $x = 'secret';
+
+    static function go($c) {
+      var_dump($c->x);
+    }
+}
+
+$c = new C(array('x'=>'public'));
+
+$c->setFlags(ArrayObject::ARRAY_AS_PROPS);
+C::go($c);
+var_dump($c->x);
+
+
+$c->setFlags(0);
+C::go($c);
+var_dump($c->x);
+?>
+--EXPECTF--
+string(6) "secret"
+string(6) "public"
+string(6) "secret"
+
+Fatal error: Uncaught Error: Cannot access private property C::$x in %s:19
+Stack trace:
+#0 {main}
+  thrown in %s on line 19