Merge class dict with parent dict when creating meta attributes

In some situations, where the Base class defines an Attribute, the
BaseMeta class doesn't properly see the _get_parent_attribute or
_get_attr_<whatever> methods because of multiple layers of subclasses
(ie. Handler, which subclasses Task). This addresses that by merging
the __dict__ of the parent with the current classes __dict__ meaning
all future iterations see available special methods.

Fixes #18378

lib/ansible/playbook/base.py

@@ -131,7 +131,9 @@ class BaseMeta(type):
             for parent in parents:
                 if hasattr(parent, '__dict__'):
                     _create_attrs(parent.__dict__, dst_dict)
-                    _process_parents(parent.__bases__, dst_dict)
+                    new_dst_dict = parent.__dict__.copy()
+                    new_dst_dict.update(dst_dict)
+                    _process_parents(parent.__bases__, new_dst_dict)
 
         # create some additional class attributes
         dct['_attributes'] = dict()