[ADF-4444] drag and drop fixes (#4674)

* more granular control over drag and drop

* fix performance, internal drop-zone directive

demo-shell/src/app/components/datatable/drag-and-drop/datatable-dnd.component.html

@@ -1,6 +1,8 @@
 <h1>DataTable Drag and Drop Demo</h1>
 <div data-automation-id="datatable"
+    (header-dragover)="onDragOver($event)"
     (header-drop)="onDrop($event)"
+    (cell-dragover)="onDragOver($event)"
     (cell-drop)="onDrop($event)">
     <adf-datatable [data]="data"></adf-datatable>
 </div>

demo-shell/src/app/components/datatable/drag-and-drop/datatable-dnd.component.ts

@@ -88,6 +88,10 @@ export class DataTableDnDComponent implements OnInit {
         this.data.setSorting(new DataSorting('id', 'asc'));
     }
 
+    onDragOver(event: CustomEvent) {
+        event.preventDefault();
+    }
+
     onDrop(event: DataTableDropEvent) {
         event.preventDefault();