[2.1.0] Views Rows source : add an option to be able to return each row as an array of visible fields

This new ui_patterns_views_rows_as_fields configuration in the ViewRowsSource plugin is not necessary because:

• there is already a system to force the fields at the View plugins level
• "fields" here are related to the API and the configuration model, not necessary the returned renderable

It would be better to catch the returned renderable from some ViewRow plugins, and to tidy it. If we want a list of renderables:

• the array must not be an associative array
• the list must not be wrapped in a useless renderable from views module