No designer for certain root element types
Not all Top Level (root) items will display a designer. Only a subset of all of the possible "root" items can have a designer displayed. When we don't support displaying a designer for the root item we will display a placeholder screen.
*""UserControl"" is not designable
*""ResourceDictionary"" is not designable
*Application is not designable
Cider currently doesn't support these root element types
*""PageFunction"" is not designable