Move _WidgetsInTemplateMixin specific code from _AttachMixin to _WidgetsInTemplateMixin.  Refs #16576 tangentially, !strict.
Move _WidgetsInTemplateMixin specific code from _AttachMixin to _WidgetsInTemplateMixin.  Refs #16576 tangentially, !strict.

git-svn-id: ee6e786acc44c9cca5ee17c71a5576c45c210361@30771 560b804f-0ae3-0310-86f3-f6aa0a117693

redaktor/deliteful