Docs feedback: Code Intelligence does not work for Java

https://docs.gitlab.com/ee/user/project/code_intelligence.html

On the Code Intelligence page, it says "View a complete list of available LSIF indexers on their website and refer to their documentation to see how to generate an LSIF file for your specific language." On LSIF.dev, lsif-java is fully supported.

However, as per #224336 (closed), Code Intelligence very much doesn't work for Java. In fact, it just silently fails, which is extremely unhelpful and can (does) lead to people wasting hours trying to debug their setup.