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/getText.ts

@@ -1,8 +1,8 @@
 import { TextSerializer } from '../types'
 import { Node as ProseMirrorNode } from 'prosemirror-model'
-import getTextBetween from './getTextBetween'
+import { getTextBetween } from './getTextBetween'
 
-export default function getText(
+export function getText(
   node: ProseMirrorNode,
   options?: {
     blockSeparator?: string,