Added note anout object habdlers API change

Author: dstogov

UPGRADING.INTERNALS

@@ -1,7 +1,7 @@
 PHP 8.0 INTERNALS UPGRADE NOTES
 
 1. Internal API changes
-  a. TBD
+  a. Object Handlers API
 
 2. Build system changes
   a. Abstract
@@ -14,7 +14,10 @@ PHP 8.0 INTERNALS UPGRADE NOTES
 1. Internal API changes
 ========================
 
- a. TBD
+ a. Object Handlers API and some related functions, e.g. zend_call_method() and
+    zend_objects_clone_obj() were changed to recieve zend_object* instead of
+    zval* and zend_string* instead of zval* for property names.
+
 
 ========================
 2. Build system changes