MC-4137: TinyMCE Issues within inline WYSIWYG

- Resolve serialisation issue

Author: davemacaulay

app/code/Magento/PageBuilder/view/adminhtml/web/js/master-format/render/serialize.js

@@ -53,5 +53,9 @@ export function getSerializedTree(contentType: ContentTypeInterface) {
  * @param contentType
  */
 function getData(contentType: ContentTypeInterface): GeneratedElementsData {
-    return contentType.dataStore.getState() || {};
+    /**
+     * Flip flop to JSON and back again to ensure all data is serializable. Magento by default adds functions into
+     * some basic types which cannot be serialized when calling PostMessage.
+     */
+    return JSON.parse(JSON.stringify(contentType.dataStore.getState())) || {};
 }