feat(core): dnd support external types (#9033)

fix AF-1847

two issues:
1. original `dropTargetForExternal` only works if dragging target is from another window context. patched the library to bypass this issue
2. `dataTransfer`'s content is only available on `drop` event. This means we cannot have `canDrop` checks for external elements (like blocksuite links).

packages/frontend/component/src/ui/dnd/draggable.ts

@@ -103,6 +103,8 @@ export const useDraggable = <D extends DNDData = DNDData>(
       },
     };
 
+    dragRef.current.dataset.affineDraggable = 'true';
+
     const cleanupDraggable = draggable({
       element: dragRef.current,
       dragHandle: dragHandleRef.current ?? undefined,