feat(editor): drag handle widget extension (#11962)

Closes: BS-3220

blocksuite/affine/widgets/drag-handle/src/view.ts

@@ -0,0 +1,21 @@
+import {
+  type ViewExtensionContext,
+  ViewExtensionProvider,
+} from '@blocksuite/affine-ext-loader';
+
+import { dragHandleWidget } from '.';
+import { effects } from './effects';
+
+export class DragHandleViewExtension extends ViewExtensionProvider {
+  override name = 'affine-drag-handle-widget';
+
+  override effect() {
+    super.effect();
+    effects();
+  }
+
+  override setup(context: ViewExtensionContext) {
+    super.setup(context);
+    context.register(dragHandleWidget);
+  }
+}