refactor: restructure extensions

packages/extension-document/src/document.ts

@@ -0,0 +1,15 @@
+import { Node } from '@tiptap/core'
+
+const Document = Node.create({
+  name: 'document',
+  topNode: true,
+  content: 'block+',
+})
+
+export default Document
+
+declare module '@tiptap/core' {
+  interface AllExtensions {
+    Document: typeof Document,
+  }
+}