MC-15375: XSS Injection via nested link in Banner

Use positive lookahead to eliminate all inner content between starting anchor tag and first instance of ending anchor tag

Author: danmooney2

app/code/Magento/PageBuilder/view/adminhtml/web/js/utils/nesting-link-dialog.js

@@ -28,7 +28,7 @@ export default function nestingLinkDialog(
     const dataStoreContent = dataStore.getState() as DataObject;
     const inlineMessage = dataStoreContent[inlineMessageField] as string;
     const linkUrl = dataStoreContent[linkUrlField] as FieldDefaultsInterface;
-    const aLinkRegex = /<a[\s]+([^>]+)>|<a>|<\/a>/igm;
+    const aLinkRegex = /(<a[\s]+[^>]+).+(?=<\/a>)<\/a>/igm;
     if (wysiwyg &&
         inlineMessage.match(aLinkRegex) &&
         linkUrl &&