When I first implemented the Efl.Container interface I made a mistake of
mixing "single slot" content API's with "multiple children" content
API's. This should fix that, by separating API's that are for a single
part and those that deal with a list of children.
Efl.Content: Single slot. This will be used a lot by efl_part()
objects, and for the default content of widgets (eg. the window
content).
Efl.Container: Multiple children. Used by lists, boxes, layouts
(edje/elm), etc...
I didn't see any class that implemented both interfaces (note: Layout
implements Container and Button implements Content, so technically
Button implements both through inheritance).
For now the eo_prefix is not changed in Efl.Container. I wonder if it
should be reset (to efl_container) or not. This would only affect the C
API.
Ref T5328