Breaking: #73044 - JSON for ClickMenu in Backend 

See forge#73044

Description 

The ClickMenu in the TYPO3 Backend now uses JSON to transport data between the server and the client.

Before, a proprietary <t3ajax> syntax with XML was used to transport the contents of the ClickMenu.

Impact 

Using ClickMenu to implement a custom ClickMenu JavaScript handler instead of the default ClickMenu.js could result in unexpected behaviour.

Affected Installations 

Installations with extensions that use custom ClickMenu.js behaviour.

Migration 

Adapt the custom code to handle JSON responses instead of XML responses.