UI catalog should include path of duplicate file in error message
If an extension attempts to add a file to the UI catalog that is already present, Antora throws an error with the message "Duplicate file". This message lacks information about which file and the fact that it's a UI file.
Here's what we would expect to see.
Duplicate UI file: js/vendor/lunr.js
Update the error message to include this additional information to help with debugging.