Disable code lens for the java file not in the project's classpath

[testforstephen]

Hello.java is not in the maven source path src/main/java, so jdt will not persist the corresponding .class file in the target directory. When the user clicks the Run/Debug code lens, it will pop up Error: Could not find or load main class Hello. This sometimes will confuse the user, it's better that the debugger doesn't show the code lens.

[testforstephen]

The fix is to keep the code lens, but clicking it will prompt to add the file to Java source path.