fix(core): canDrop check for external (#9058)

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

@@ -0,0 +1,13 @@
+import { createContext } from 'react';
+
+import type { DNDData, ExternalDataAdapter } from './types';
+
+export const DNDContext = createContext<{
+  /**
+   * external data adapter.
+   * if this is provided, the drop target will handle external elements as well.
+   *
+   * @default undefined
+   */
+  externalDataAdapter?: ExternalDataAdapter<DNDData>;
+}>({});