Improve messages when no JDK 11+ found to launch language server

[Eskibear]

from #1672 (comment)

It's reported that the message is confusing to highlight java.configuration.runtimes instead of java.home.

At this point the user is more concerned with installing the Java extension than compiling future projects with old JDKs.
I would suggest updating the message and focusing on the java.home setting since it is something that the user must currently update to use the extension.

[Eskibear]

Closing as completed. #2183 moved platform builds to an embedded JRE, so the original JDK 11 launch prompt is obsolete.