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

* wip: implement datatransfer

* Editable kanban contents

* desktop sorta works without crashing

* lint

Cargo.toml

@@ -790,6 +790,11 @@ name = "websocket"
 path = "examples/07-fullstack/websocket.rs"
 doc-scrape-examples = true
 
+[[example]]
+name = "drag_and_drop"
+path = "examples/08-apis/drag_and_drop.rs"
+doc-scrape-examples = true
+
 [[example]]
 name = "control_focus"
 path = "examples/08-apis/control_focus.rs"