Remove all Path Filtering from Drag and Drop

Fixes #9096 

@peterflynn -- This was done intentionally because we didn't throw error messages when dragging images onto brackets. We just silently bailed. It seemed to make sense that we wouldn't throw an error for files that can't be opened.  

I wonder if we some drag and drop tests to our smoke test script?
Modules we don't need any longer: MainViewFactory, LanguageManager, EditorManager, FileUtils