chore(editor): add feature flag entry for testing turbo renderer (#10581)

The debug pane will be displayed once the `enable_turbo_renderer` feature flag is enabled.

![image.png](https://graphite-user-uploaded-assets-prod.s3.amazonaws.com/lEGcysB4lFTEbCwZ8jMv/c1ba558a-2d84-403c-aa81-864b0338c861.png)

blocksuite/blocks/src/index.ts

@@ -100,6 +100,10 @@ export {
   SpecProvider,
   stopPropagation,
 } from '@blocksuite/affine-shared/utils';
+export {
+  ViewportTurboRendererExtension,
+  ViewportTurboRendererIdentifier,
+} from '@blocksuite/affine-shared/viewport-renderer';
 export type { DragBlockPayload } from '@blocksuite/affine-widget-drag-handle';
 
 const env: Record<string, unknown> =