RecursiveTreeIterator::__construct(): switch @param to typehint (php#16215)

The type is enforced, and `TypeError`s are already thrown, but the
information about the required type is not provided to Reflection. Replace the
`@param` comment with a real typehint so that the information is also available
via Reflection.

Author: DanielEScherzer

ext/spl/spl_iterators.stub.php

@@ -422,9 +422,8 @@ class RecursiveTreeIterator extends RecursiveIteratorIterator
 
     public const int PREFIX_RIGHT = 5;
 
-    /** @param RecursiveIterator|IteratorAggregate $iterator */
     public function __construct(
-        $iterator,
+        RecursiveIterator|IteratorAggregate $iterator,
         int $flags = RecursiveTreeIterator::BYPASS_KEY,
         int $cachingIteratorFlags = CachingIterator::CATCH_GET_CHILD,
         int $mode = RecursiveTreeIterator::SELF_FIRST