refactor: recreate extension exports

packages/extension-underline/src/index.ts

@@ -0,0 +1,5 @@
+import { Underline } from './underline'
+
+export * from './underline'
+
+export default Underline

packages/extension-underline/src/underline.ts

@@ -6,7 +6,7 @@ export interface UnderlineOptions {
   },
 }
 
-const Underline = Mark.create({
+export const Underline = Mark.create({
   name: 'underline',
 
   defaultOptions: <UnderlineOptions>{
@@ -58,8 +58,6 @@ const Underline = Mark.create({
   },
 })
 
-export default Underline
-
 declare module '@tiptap/core' {
   interface AllExtensions {
     Underline: typeof Underline,