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___construct_basic1.phpt

@@ -0,0 +1,58 @@
+--TEST--
+SPL: ArrayObject::__construct basic usage.
+--FILE--
+<?php
+echo "--> No arguments:\n";
+var_dump(new ArrayObject());
+
+echo "--> Object argument:\n";
+$a = new stdClass;
+$a->p = 'hello';
+var_dump(new ArrayObject($a));
+
+echo "--> Array argument:\n";
+var_dump(new ArrayObject(array('key1' => 'val1')));
+
+echo "--> Nested ArrayObject argument:\n";
+var_dump(new ArrayObject(new ArrayObject($a)));
+?>
+--EXPECTF--
+--> No arguments:
+object(ArrayObject)#1 (1) {
+  ["storage":"ArrayObject":private]=>
+  array(0) {
+  }
+}
+--> Object argument:
+
+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
+object(ArrayObject)#2 (1) {
+  ["storage":"ArrayObject":private]=>
+  object(stdClass)#1 (1) {
+    ["p"]=>
+    string(5) "hello"
+  }
+}
+--> Array argument:
+object(ArrayObject)#2 (1) {
+  ["storage":"ArrayObject":private]=>
+  array(1) {
+    ["key1"]=>
+    string(4) "val1"
+  }
+}
+--> Nested ArrayObject argument:
+
+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
+
+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
+object(ArrayObject)#2 (1) {
+  ["storage":"ArrayObject":private]=>
+  object(ArrayObject)#3 (1) {
+    ["storage":"ArrayObject":private]=>
+    object(stdClass)#1 (1) {
+      ["p"]=>
+      string(5) "hello"
+    }
+  }
+}