[Nested widgets] Outer widget's drag handler is not created if it has any nested widgets

[Piotrek Koszuliński]

Part of: #10931.

1. Open plugins/widget/dev/nestedwidgets.html
2. See that simple boxes don't have drag handlers.

The reason is that we try to find existing drag handler by findOne( '.cke_widget_drag_handler_container' ), so since nested widgets are already initialised while we do this, we find their handlers.

Note that changing order will not solve the issue because when pasting all widgets have drag handlers, so we'll find them anyone. And not necessarily the one we get from findOne is the main widget's handler.

[Piotrek Koszuliński]

Pushed ​branch:t/12022 on dev and tests.

I found an issue with outline and drag handler on FF though. Unpositioned handlers of nested widgets extends outline to the left (they are hidden outside of the view port).

[Piotrek Koszuliński]

Fixed on master with ​git:d50ebea on dev and 16e2fbc on tests.