FactoryLists: rework iterating methods
eg gst::ElementFactory::list_get_elements
returns a Vec gst::ElementFactory::list_filter
expects a &[] and returns a Vec, that's all a bit suboptimal :)
eg gst::ElementFactory::list_get_elements
returns a Vec gst::ElementFactory::list_filter
expects a &[] and returns a Vec, that's all a bit suboptimal :)