MDL-79829 core: Reactive drag and drop cursor

* When dragging and dropping an item, the cursor should be
set to "move" and not copy.

lib/amd/src/local/reactive/dragdrop.js

@@ -283,7 +283,7 @@ export default class extends BaseComponent {
             position.y = event.offsetY;
         }
         event.dataTransfer.setDragImage(dragImage, position.x, position.y);
-
+        event.dataTransfer.effectAllowed = 'copyMove';
         this._callParentMethod('dragStart', dropdata, event);
     }
 
@@ -347,6 +347,7 @@ export default class extends BaseComponent {
      */
     _dragOver(event) {
         const dropdata = this._processEvent(event);
+        event.dataTransfer.dropEffect = (event.altKey) ? 'copy' : 'move';
         if (dropdata && !this.dropzonevisible) {
             this.dropzonevisible = true;
             this.element.classList.add(this.classes.DRAGOVER);