refactor: Use named exports instead of default exports (#2238)

* use named exports instead of default exports

* fix tests

Co-authored-by: Philipp Kühn <philippkuehn@MacBook-Pro-von-Philipp.local>

packages/core/src/helpers/isNodeEmpty.ts

@@ -1,6 +1,6 @@
 import { Node as ProseMirrorNode } from 'prosemirror-model'
 
-export default function isNodeEmpty(node: ProseMirrorNode): boolean {
+export function isNodeEmpty(node: ProseMirrorNode): boolean {
   const defaultContent = node.type.createAndFill()?.toJSON()
   const content = node.toJSON()