refactor(editor): extract root block (#10356)

Closes: [BS-2207](https://linear.app/affine-design/issue/BS-2207/move-root-block-to-affineblock-root)

blocksuite/affine/block-root/src/root-config.ts

@@ -0,0 +1,12 @@
+import { ConfigExtensionFactory } from '@blocksuite/block-std';
+
+import type { KeyboardToolbarConfig } from './widgets/keyboard-toolbar/config.js';
+import type { LinkedWidgetConfig } from './widgets/linked-doc/index.js';
+
+export interface RootBlockConfig {
+  linkedWidget?: Partial<LinkedWidgetConfig>;
+  keyboardToolbar?: Partial<KeyboardToolbarConfig>;
+}
+
+export const RootBlockConfigExtension =
+  ConfigExtensionFactory<RootBlockConfig>('affine:root-block');