Description:
------------
There is no way of making sure that a parameter is an object.

Since there is a type hint for many `is_*()` functions, there should be one for objects too - maybe just `\stdClass`?

Test script:
---------------
<?php
function acceptsObject(\stdClass $o) {}
$anonymousObject = new class() {};

acceptsObject(new DOMDocument());
acceptsObject($anonymousObject);

Actual result:
--------------
PHP Fatal error:  Uncaught TypeError: Argument 1 passed to acceptsObject() must be an instance of stdClass, instance of DOMDocument given, called in /tmp/test.php on line 5 and defined in /tmp/test.php:2
Stack trace:
#0 /tmp/test.php(5): acceptsObject(Object(DOMDocument))
#1 {main}
  thrown in /tmp/test.php on line 2

Fatal error: Uncaught TypeError: Argument 1 passed to acceptsObject() must be an instance of stdClass, instance of DOMDocument given, called in /tmp/test.php on line 5 and defined in /tmp/test.php:2
Stack trace:
#0 /tmp/test.php(5): acceptsObject(Object(DOMDocument))
#1 {main}
  thrown in /tmp/test.php on line 2