datatransfer object, drag_and_drop example, fix drag-and-drop (#4789)

* wip: implement datatransfer

* Editable kanban contents

* desktop sorta works without crashing

* lint

packages/html/src/lib.rs

@@ -25,10 +25,12 @@ pub mod events;
 pub(crate) mod file_data;
 pub use file_data::*;
 mod attribute_groups;
+mod data_transfer;
 pub mod geometry;
 pub mod input_data;
 pub mod point_interaction;
 mod render_template;
+pub use data_transfer::*;
 
 pub use bytes;