refactor(editor): extract markdown adapter (#9443)

blocksuite/blocks/src/index.ts

@@ -7,6 +7,7 @@ import { splitElements } from './root-block/edgeless/utils/clipboard-utils.js';
 import { isCanvasElement } from './root-block/edgeless/utils/query.js';
 
 export * from './_common/adapters/index.js';
+export * from './_common/adapters/markdown';
 export { type NavigatorMode } from './_common/edgeless/frame/consts.js';
 export {
   ExportManager,
@@ -108,6 +109,9 @@ export {
   ImageAdapter,
   ImageAdapterFactoryExtension,
   ImageAdapterFactoryIdentifier,
+  MarkdownAdapter,
+  MarkdownAdapterFactoryExtension,
+  MarkdownAdapterFactoryIdentifier,
   NotionTextAdapter,
   NotionTextAdapterFactoryExtension,
   NotionTextAdapterFactoryIdentifier,